■.j'HiiwiinHnnnouummnwK 



m»immm \ w ■ii i i»)i i !i i i | i!i|iiii > i;i i | i i « |W M» « «ww ^ ^ 

■iiiiiw|i;ilii!i>ki|iiiiiiii<wiu>iM»<|i>iiii;iniiMii.iniliiiiani}«m)'<l 






Class 



S r>cij 



Book... 



Cop)^§htN^_ 



CDPVRIGKT DEPOSm 



XTbe IRural Science Series 

Edited by L. H. BAILEY 



THE BREEDING OF ANIMALS 



W^t Eural Science Series 

Edited by L. H. Bailey 

The Soil. King. 

The Spraying of Plants. Lodeman. 

Milk AND ITS Products. Wing. Enlarged and Bevised. 

The Fertility of the Land. Boberts. 

The Principles of Fruit-growing. Bailey. 20th 

Edition., Bevised. 
Bush-fruits. Card. Bevised. 
Fertilizers. Voorhees. Bevised. 
The Principles of Agriculture. Bailey. Bevised. 
Irrigation and Drainage. King. 
The Farmstead. Boberts. 
Rural Wealth and Welfare. Fairchild. 
The Principles of Vegetable-gardening. Bailey. 
Farm Poultry. Watson. Enlarged and Bevised. 
The Feeding of Animals. Jordan. (Now Rural 

Text-Book Series. ) 
The Farmer's Business Handbook. Boberts. 
The Diseases of Animals. Mayo. 
The Horse. Boberts. 
How TO Choose a Farm. Hunt. 
Forage Crops. Voorhees. 

Bacteria in Relation to Country Life. Lipman. 
The Nursery-book. Bailey. 
Plant-breeding. Bailey and Gilbert. Bevised. 
The Forcing-book. Bailey. 

The Pruning-book. Bailey. (Now Rural Manual Series.) 
Fruit-growing in Arid Regions. Paddock and Whipple. 
Rural Hygiene. Ogden. 
Dry-farming. Widtsoe. 
Law for the American Farmer. Green. 
Farm Boys and Girls. McKeever. 
The Training and Breaking of Horses. Harper. 
Sheep-farming in North America. Craig. 
Cooperation in Agriculture. Powell. 
The Farm Woodlot. Cheyney and Wentling. 
Household Insects. Herrick. 
Citrus Fruits. Coit. 

Principles of Rural Credits. Morman. 
Beekeeping. Phillips. 

Subtropical Vegetable-gardening. Bolfs. 
The Potato. Gilbert. 



THE 



BREEDmG OF ANIMALS 




Ft BrMUMFORD, M.S. 



DEAN OF THE COLLEGE OF AGRICULTURE AND 

DIRECTOR OF THE EXPERIMENT STATION 

OF THE UNIVERSITY OF MISSOURI 



THE MACMILLAN COMPANY 
1917 

All rights I'eserved 



. II s 



Copyright, 1917, 
By the MACMILLAN COMPANY. 



Set up and electrotyped. Published February, 1917. 



MAR -I lyl7 



J. S. Cashing Co. — Berwick & Smith Co. 
Norwood, Mass., U.S.A. 



S)C1..A457249 



PREFACE 

The problems of the animal-breeder may all be 
grouped under the three subjects, reproduction, inherit- 
ance, development. The mere multiplication of the 
species is now, and always has been, the major work of 
the breeder of domestic animals. But the real breeder 
is not only concerned with the production of mere 
numbers of animals of a given species but is primarily 
interested in securing animals possessing the largest 
number of desirable qualities and the least number of 
qualities undesirable to man. 

How to maintain the good qualities that have already 
appeared in an individual, and how to cause other and 
better qualities to become dominant in future indi- 
viduals of the same species, is the problem of inheritance 
that chiefly concerns the breeder of the domestic ani- 
mals. The highest attainments in the breeder's art 
have come only to those who have had a good knowl- 
edge of the principles and laws of heredity. The de- 
velopment of animals from the fertilization of the egg 
to maturity and their proper maintenance throughout 
their productive lives is second in importance only to 
inheritance. The environment of the animal, including 
food, climate, and exercise of functions, determines the 
degree of development in the individual animal. The 
term Development, as used in this connection, has refer- 
ence to the unfolding of capabilities that have come to 
the animal through inheritance. 



vi PREFACE 

The author has made no attempt to write a book on 
genetics or evolution ; but the principles of genetics as 
they apply to the practice of animal-breeding are dis- 
cussed, in accordance with the conclusions of biologists. 
The problems of the animal-breeder are in many im- 
portant particulars widely different from those of the 
plant-breeder ; and the emphasis has been placed on 
those principles and practices that belong peculiarly to 
the province of the animal-breeder, while not neglecting 
the lessons and illustrations to be drawn from the other 
field. 

It has been the purpose to make a practical book 
which shall be directly useful to the student and to the 
breeder of animals, and the lessons and examples of 
which can be applied in the laboratory and on the farm. 



F. B. MUMFORD. 



Columbia, Mo. 

November, 1916. 



TABLE OF CONTENTS 



CHAPTER I 

PAGES 

The Cell 1-15 

The cell theory, 1 ; The germ-cells, 2 ; The cell, 3 ; Is 
the cell the physiological unit ? 4 ; The structure of the 
cell, 5 ; Protoplasm, 6 ; The nucleus, 7 ; Growth by cell 
division, 8 ; How cells divide, 9 ; Prophase, 10 ; Meta- 
phase, 11 ; Anaphase, 12 ; Telophase, 13; The germ-cells 
in detail, 14 ; The ovum, 15 ; The spermatozoon, 16. 

CHAPTER II 

Reproduction ......... 16-51 

Asexual reproduction, 17 ; Sexual reproduction, 18 ; 
The reproductive process, 19 ; Oviparous animals, 20 ; 
Primary and secondary sexual characters, 21 ; The re- 
productive organs of the male, 22 ; The testicles, 23 ; 
Castration, 24; The reproductive organs of the female, 
25 ; The ovaries, 26 ; The Fallopian tubes, 27 ; The 
uterus, 28 ; The mammary glands, 29 ; Structure of 
mammary glands, 30 ; Pertilization of the ovum, 31 ; 
The nature of fertilization, 32 ; The process of fertiliza- 
tion, 33 ; The chromosomes, 34 ; Results of the union of 
egg and sperm, 35 ; Changes in the ovum, 36 ; Changes 
in the spermatozoon, 37 ; The significance of reduction, 
38 ; The origin of the germ-cells, 39 ; Maturation and 
reduction in the female (oogenesis), 40 ; Reduction in 
the male (spermatogenesis), 41 ; The period of the 
oestrum or heat, 42 ; Artificial insemination, 43 ; Meth- 
ods of artificial insemination, 44 ; Conditions influenc- 
ing the vitality of the sperm-cells, 45 ; Effect of too 

vii 



viii TABLE OF CONTENTS 

PAOE8 

frequent breeding on the sperm-cells, 46 ; Vitality of 
spermatozoa within the female generative organs, 47 ; 
Effect of intoxication of the male parent on his off- 
spring, 48 ; Effect of lead poisoning on the male germ- 
cells as indicated by the offspring, 49. 

CHAPTER III 

The Breeding Season 52-66 

Changed conditions, 50 ; Phases of the breeding sea- 
son, 51 ; Prooestrum, 62 ; Oestrum, 53 ; Metoestrum, 54 ; 
Dicestrum, 55 ; Puberty, 56 ; Conditions influencing 
puberty, 57 ; The oestrum and lactation, 58 ; Heat dur- 
ing pregnancy, 59 ; Superfoetation, 60 ; Examples of 
superfoetation, 61 ; Recurrence and duration of the 
oestrum, 62 ; Effect of ration on recurrence of oestrum, 63. 

CHAPTER IV 
Gestation and Lactation ....... 66-84 

Gestation : Indications of pregnancy, 64 ; Physical 
examination for pregnancy, 65 ; The period of gestation, 
66 ; Causes of variation in length of gestation period, 67 ; 
Incubation, 68 ; Parturition, 69 ; Normal parturition of 
the domestic animals, 70 ; Mal-presentations, 71 ; Normal 
presentations, 72 ; Treatment for mal-presentation, 73. 

Lactation : The mammary glands, 74 ; The duration 
of lactation, 75 ; The food supply, 76 ; Habit, 77 ; He- 
redity, 78 ; Exercise, 79 ; Climate, 80 ; Unusual lacta- 
tion, 81. 

CHAPTER V 
Fertility .......... 85-112 

The number of young at a birth, 82 ; Period of gesta- 
tion and fertility, 83 ; Fertility and the frequency of the 
recurrence of the oestrum, 84 ; Fertility and gestation, 85 ; 
Duration of the reproductive period, 86; Confinement 
and fertility, 87 ; The fertility of domesticated animals, 
88 ; Age and fertility, 89 ; Relation of age to fertility in 



TABLE OF CONTENTS IX 

PAGES 

swine, 90 ; Influence of age of sow on size of litter, 91 ; Re- 
lation of age to fertility in sheep, 92 ; Influence of age 
of ram on fertility of ewes, 93 ; The effect of the age of 
poultry parents on the offspring, 94 ; Age and fecundity, 
95 ; Nutrition and fertility, 96 ; Excessive food supply 
and nutrition, 97 ; Other factors affecting fertility, 98 ; 
Relation of number of mammae in swine to fertility, 99 ; 
Twins, 100 ; Characters correlated with fertility, 101 ; In- 
breeding and fertility, 102 ; Cross-breeding and fertility, 
103 ; Unusual fertility, 104 ; Unusual fertility among 
horses, 105 ; Unusual fertility among cattle, 106 ; Un- 
usual fertility among sheep, 107 ; Unusual fertility 
among swine, 108 ; Unusual fertility among poultry, 109. 

CHAPTER VI 

Sterility 113-130 

The causes of sterility, 110 ; Causes of sterility in the 
male. 111 ; Sterility in the female, 112 ; Closure of the 
cervix, 113 ; Obstruction of Fallopian tubes resulting 
from excessive fatness, 114 ; Other causes of barrenness, 
115 ; Sterility from fatty degeneration, 116 ; Sterility 
caused by abortion, 117 ; Contagious abortion and ste- 
rility, 118 ; Treatment for contagious abortion, 119 ; 
Diagnosis of contagious abortion, 120 ; The complement 
fixation test, 121 ; Sterility of free-martins, 122. 

CHAPTER VII 

Heredity 131-156 

Development, 123 ; Heredity defined, 124 ; Heredity 
and variation not antagonistic, 125; The kinds of he- 
redity, 126 ; Blending inheritance, 127 ; Alternative in- 
heritance, 128 ; Particulate or mosaic inheritance, 129 ; 
Mendelian inheritance, 130 ; The experiments of Men- 
del, 131 ; The law of dominance, 132 ; The law of seg- 
regation, 133; Unit characters, 134; Gametic purity, 
135 ; Application of Mendel's law, 136 ; The complexity 
of animal characters, 137 ; The inheritance of polled and 
horned character in cattle, 138 ; Theory of pure lines, 



X TABLE OF CONTENTS 

PAGES 

139 ; Hallett's wheat breeding, 140 ; The presence and 
absence hypothesis, 141 ; The theory of mutations, 142 ; 
Two important classes of variation, 143 ; Kinds of muta- 
tions, 144 ; Importance of the mutation theory, 145 ; 
Mono-hybrids and di-hybrids, 146. 

CHAPTER VIII 

Inheritance of Acquired Characters .... 157-182 
Belief in transmission of acquired characters, 147 ; 
Practical breeders believe in transmission of acquired 
characters, 148 ; Nature and nurture, 149 ; What are 
acquired characters ? 150 ; Somatoplasm and germ- 
plasm, 151 ; Examples of acquired characters, 152 ; Food 
supply, 153 ; Influence of the amount of food on body 
weight, 154 ; Food supply and body changes, 155 ; In- 
fluence of limited food supply from birth, 156 ; Teleg- 
ony, 157 ; The Lord Morton mare, 158 ; The Penycuik 
experiments, 159 ; Telegony and mule hybrids, 160 ; 
Example of horse foals, 161 ; Possibility of influence 
from a previous impregnation, 162; Xenia in animals, 
163 ; Xenia among poultry, 164. 

Objections to the Theory that Acquired Characters are 
Transmitted : No mechanism for the inheritance of ac- 
quired characters, 165 ; The inheritance of disease, 166 ; 
Acquired diseases, 167 ; Congenital disease, 168 ; Pre- 
disposition to disease, 169; Immunity, 170. 



CHAPTER IX 

Heredity and Sex 183-194 

The significance of conjugation and fertilization, 171 ; 
Secondary sexual characters, 172 ; Secondary sexual 
characters and vigor, 173 ; Effects of castration and 
ovariotomy on the secondary sexual characters, 174 ; 
Effect of transplanting sexual glands, 175 ; Effect of 
internal secretion, 176 ; Sex-linked characters, 177 ; 
Color-blindness, 178 ; Controlling the sex of offspring, 
179 ; Age or vigor of parents, 180 ; Comparative vigor ov 



TABLE OF CONTENTS XI 

PAGES 

sexual superiority, 181 ; Nutrition and sex, 182 ; The 
maturity of the ovum, 183 ; Seasonal variations in pro- 
portion of sexes, 184 ; Sex cannot be controlled by ex- 
ternal conditions, 185. 

CHAPTER X 

Variation 195-216 

Importance of variability, 186 ; Morphological varia- 
tions, 187 ; Physiological variations, 188 ; Meristic vari- 
ation, 189 ; Functional variations, 190 ; Examples of 
functional variation, 191 ; Variation in fertility of ani- 
mals, 192 ; Variation in the milking function, 193 ; 
Variations among different cows, 194 ; New characters 
originate in the germ-plasm, 195 ; Mutilations, 196 ; The 
Brown-Sequard experiments, 197 ; Causes of variation, 
198 ; Cell division a cause of variation, 199 ; Influence 
of use and disuse in causing modifications, 200 ; Im- 
portance of causes of variation to the breeder of domes- 
tic animals, 201 ; Germinal variations, 202. 

CHAPTER XI 

In-breeding 217-242 

Definitions, 203 ; Advantages claimed for in-breeding, 
204 ; Bad results from in-breeding, 205 ; Decreased fer- 
tility and vigor from in-breeding, 206 ; Darwin's re- 
searches, 207 ; In-breeding cattle, 208 ; The Chillingham 
cattle, 209; Deer in parks, 210; In-breeding among pigs, • 
211 ; In-breeding sheep, 212 ; In-breeding dogs, 213 ; 
Cornevin's experiments, 214 ; Weismann's and Von 
Guaita's experiments, 215 ; Researches of Ritzema Bos, 
216 ; The Wistar Institute experiments, 217 ; In-breeding 
Berkshires by Mr. Gentry, 218 ; In-breeding corn, 219 ; 
How long is it safe to continue in-breeding ? 220 ; Selec- 
tion important, 221 ; The truth about in-breeding, 222 ; 
Fixing characters by in-breeding, 223 ; In-breeding and 
prepotency, 224 ; Results of in-breeding vary with dif- 
ferent species, 225. 



xii TABLE OF CONTENTS 

CHAPTER XII 

PAGES 

Cross-breeding 243-254 

Permanent and temporary results of cross-breeding, 
226 ; Advantages from cross-breeding, 227 ; Grading, 
228 ; Cross-breeding to increase fertility, 229 ; Cross- 
breeding to increase size and restore constitution, 230 ; 
Crossing and heredity, 231 ; First cross and improve- 
ment, 232 ; Cross-breeding as a cause of variation, 233 ; 
Crossing species, 234 ; Crossing bison and cattle, 235 ; 
The mule hybrid, 236 ; The hinny hybrid, 237 ; Cross- 
ing the horse and the zebra, 238 ; Crossing cattle and 
zebu, 239 ; Sheep-goat hybrid, 240. 

CHAPTER XIII 
Development ......... 255-279 

Growth, 241 ; The growth impulse, 242 ; Factors in- 
fluencing growth, 243 ; Growth and food supply, 244 ; 
Capacity to grow, 246 ; Growth and the cell, 246 ; When 
the growth impulse is strongest, 247 ; Development of 
the foetus, 248 ; Heredity and foetal development, 249 ; 
Birth weight of lambs, 250 ; Effect of protein and ash in 
ration on foetal development, 251 ; High calcium rations 
for pregnant swine, 252 ; Size and vigor of foetus as in- 
fluenced by corn and wheat rations, 253 ; The perma- 
nent effect of retarded growth, 254 ; Early stunting and 
the capacity to grow, 255 ; Climate, 256 ; The age factor 
in animal-breeding, 257 ; Premature breeding decreases 
size, 258 ; Decreased size due to early breeding not in- 
herited, 259 ; Influence of early pregnancy on the 
mother, 260 ; Gestation and lactation in relation to 
growth, 261 ; The Missouri experiments, 262. 

CHAPTER XIV 
The Practice of Breeding . . . . . . 280-303 

Improvement in size, 263; Improvement in function, 
264 ; The milking function, 265 ; Improvement in wool 
production, 266 ; Improvement in tendency to lay on fat. 



TABLE OF CONTENTS xiii 

267 ; Improvement in speed, 268 ; Selection, 269 ; Natu- 
ral selection, 270 ; Methodical selection, 271 ; Im- 
portance of selection in animal-breeding, 272 ; Aids to 
selection, 273 ; The real results of selection in the im- 
provement of the domestic animals, 274; Selection 
within pure lines, 275 ; Vilmorin's pure line wheat- 
breeding, 276 ; Selection most useful when genetic fac- 
tors are not pure, 277 ; Pure line theory not opposed to 
improvement by selection, 278 ; Pedigree, 279 ; Regis- 
tered breeding animals, 280 ; Registry associations, 281 ; 
Community breeding, 282 ; Importance of numbers, 
283 ; Selecting the best, 284 ; Selecting chance varia- 
tions, 286 ; The Burbank method, 286 ; The mendelian 
method, 287. 



ILLUSTKATIONS 



FIG. 

1. Cell division. Prophases. Aftei* Wilson 

2. Cell division. Later phases. After Wilson 

3. The ovarian egg 

4. Human spermatozoa .... 

6. Genital organs of boar. After EUenberger 

6. Sections through ovary of rat 

7. Genital organs of mare. After EUenberger 

8. Genital organs of cow. After EUenberger 

9. Genital organs of sow. After EUenberger 

10. Genital organs of bitch. After EUenberger 

11. Normal presentation in mare 

12. Posterior presentation . 

13. Abnormal anterior presentation . 

14. Abnormal posterior presentation . 

15. Abnormal transverse presentation 

16. Diagram illustrating mendelian inheritance 

17. Diagram illustrating mendelian inheritance 



PAGE 

9 
11 
13 
14 
21 
25 
26 
29 
30 
32 
76 
77 
78 
78 
79 
140 
145 



PLATE 
I. 
II. 
III. 

IV. 

V. 

VI. 



PLATES 

Genital organs of mare. After EUenberger 
Superfcetation in mare .... 
Upper : A mare mule that secretes milk . 
Lower : A Free-Martin heifer . 
Unusual fertility in a cow. Triplet calves 
Normal healthy uterus of sow . 
Uterus of sterile sow 



FACING PAGE 


. 43 




62^ 




84^, 




84^ 




. 108 




118 ' 




119 *^ 



XV 



XVI 



ILLUSTRATIONS 



PLATE FA{ 

VII. Upper: Steer fed ration not restricted 

Lower : Steer fed greatly restricted ration 
VIII. Upper : Steer fed ration not restricted 
Lower : Steer fed for normal growth . 
IX. Upper : Steer fed generously, at age 120 days . 
Lower : Same at age 27 months .... 
X. Upper : Dam of seven mule foals followed by filly foal 

Lower : Filly foal born after seven mule foals . 
XL Upper : Eleventh foal following ten mule foals . 
Lower : Dam of ten mule foals and their filly foal 
XII. Upper : Ninth foal following eight mule foals . 

Lower : Foaled after eight mule foals in succession 

XIII. Upper : Twelfth foal following eleven mule foals 
Lower : Mother of eleven mule foals and their horse 

foal 

XIV. Upper : Close in-breeding of fox terrier 
Lower : Eighth generation of intense in-breeding 

XV. In-bred Berkshire ...... 

XVI. Cross-bred Hereford-Aberdeen Angus steer 
XVII. Upper: Half-blood buffalo (bison) heifer . 

Lower : Cross-bred buffalo-cattle bulls 
XVIII. Upper : A five-year-old hinny .... 

Lower : Sheep-goat hybrid ..... 

XIX. Effect of food supply on development. Side view 

XX. Same. Front view 

XXI. Effect of starvation on capacity to grow 
XXII. Recovery from starvation 

XXIII. Upper : Cow fed corn products .... 
Lower : Calf from cow fed corn products . 

XXIV. Upper : Cow fed wheat products 
Lower : Calf from cow fed wheat products 

XXV. Permanent effect of retarded growth . 

XXVI. Grace Briggs at age 18 years .... 

XXVII. Duchess Skylark Ormsby 

XXVIII. Sophie 19th of Hood Farm 

XXIX. Daughters of the same sire ..... 

XXX. Three generations showing impressive character of 
original dam ...... 

XXXI. Result of using a pure-bred sire .... 

XXXII. Result of using a scrub sire .... 



ACKNOWLEDGMENTS 

The author is indebted to R. Pearl for Plate IV, to 
J. W. Connaway for Plates V and VI, to P. F. Trow- 
bridge for Plates VII, VIII, IX, XXI, XXII, and XXV, 
to E. A. Trowbridge for Plate XVI, to M. Boyd for 
Plate XVII, to L. Monsees for Plate XVIII upper, to 
W. J. Spillman for Plate XVIII lower, to Hart et al, 
for Plates XXIII and XXIV, to C. H. Eckles for 
Plates XXVI, XXIX, and XXX, and to H. Hackedorn 
for Plates XXXI and XXXII. 

Grateful acknowledgment is made to all these persons 
for their valuable assistance. 



XVll 



THE BREEDING OF ANIMALS 



CHAPTER I 
THE CELL 

The greatest modern contribution to the science of 
animal-breeding was the formulation of the so-called 
cell theory. This fundamental biological generalization 
ranks with the evolution theory in importance in many 
respects ; it has given a definite physical basis for in- 
heritance. 

1. The cell theory. — All the higher forms of life are 
made up of cell units, and from these all parts of the 
body are constructed. Although various in form, all 
living cells are alike in having within a mass of proto- 
plasm which Huxley called the '' physical basis of life." 
In the simple one-celled forms all functions are found in 
the one cell, but in the more complex higher forms a 
physiological division of labor results in the distribution 
of functions among the cells. ''It is to the cell," says 
Verworn,^ '' that the study of every bodily function 
sooner or later drives us. In the muscle cell lies the 
problem of the heart beat and that of muscular con- 
traction ; in the gland cell reside the causes of secretion ; 
in the epithelial cell, in the white blood cell, lies the 
problem of absorption of food, and the secrets of the 

1 Wilson, " The Cell," p. 6, 1911. 

B 1 



2 THE BREEDING OF ANIMALS 

mind are hidden in the ganglion cell." It is now clearly- 
apparent that the great questions of reproduction, in- 
heritance and development, involving as they do the 
problems of embryology and evolution, are intricately 
bound up with the structure and functions of the cell. 

2. The germ-cells. — The heritage of the species is 
contained within the germ-cell. The microscopic egg of 
the female carries within its minute structure the germ 
characters of all the maternal ancestors. The germ-cell 
of the male, the spermatozoon, holds within its exceed- 
ingly minute compass the sum total of all the heritable 
characteristics of the paternal ancestors. All cells are 
derived from other cells. Virchow's claim made in 1855 
that every cell must have been formed by cell division 
from some previously formed cell, has now been definitely 
established. Not only does growth and development 
take place by cell division in the fertilized egg-cell, but 
the egg-cell itself is directly derived by cell division from 
an egg-cell of the immediately preceding generation, and 
so on indefinitely. 

3. The cell. — The cell is a mass of protoplasm con- 
taining a nucleus, and both nucleus and protoplasm arise 
through division of the corresponding elements of a pre- 
existing cell.^ 

The word cell is derived from the Greek and means a 
hollow chamber. The term came into common use be- 
fore the form and structure of the cell were well under- 
stood. The cell-wall which is characteristic of most 
cells is not an essential part of its structure. It is also 

1 Wilson, "The Cell in Development and Inheritance," p. 19, 
1906. 

Ley dig, " Lehrbuch der Histologie," p. 9, 1857. 
Schultze, "Arch. Anat. u. Phys.," p. 11, 1861. 



THE CELL 3 

true that living cells are never hollow chambers, but are 
filled in whole or in part by a colorless, viscid, semi-fluid 
substance, protoplasm. Many cells are simply masses 
of protoplasm lacking entirely any kind of an enclosing 
wall. Lying within the protoplasm is a minute body of 
spherical form which is the cell nucleus. These two, 
the protoplasm and the nucleus, are of universal occur- 
rence and are the essential components of a living cell. 

4. Is the cell the physiological unit ? — A study of the 
form and function of the cell leads to the inevitable 
conclusion that in a very real sense the cell is the mor- 
phological unit of the organism. In its physiological 
relations to the cells* of the body as a whole, however, 
it is not to be regarded as an independent unit but rather 
as a localized center of bodily activities. The individual 
cell in a multicellular body is influenced, sometimes in 
a marked degree, by the surrounding cells. The most 
fundamental problem in growth and development of 
animals is what and how much influence do the body- 
cells of one group have over the cells of another group. 
Is there a physiological connection between adjoining 
cells? Can a group of cells forming a so-called system 
like the reproductive system in the animal body be in- 
fluenced by the soma or body-cells ? If influenced at all, 
can such influence have any effect upon the germ plasm 
in the nucleus of the germ-cell ? Is it probable that the 
germ characters may be changed by these influences so 
that the offspring of the parent bodies where these in- 
fluences have been at work, will correspond in any way 
to the changes occurring in the parent body? In other 
words, are acquired habits transmitted ? It is to be re- 
gretted that the microscopic study of the cell has thrown 
little light upon this fundamental question. As indicated 



4 THE BREEDING OF ANIMALS 

above, the cell in the animal body is in more or less close 
physiological relation with the other cells of the body, 
but these relationships and their bearings upon- the 
fundamental facts of biology have not yet been clearly 
determined. 

5. The structure of the cell. — The cell contains a 
cell-body and the nucleus. The cell-body is all that 
portion of the protoplasm not contained in the nucleus. 
The cell in its simplest form is a rounded mass of proto- 
plasm. This type is found generally in one-celled forms 
and is the characteristic form of the egg-cell of the higher 
animals. The fact that the form of cells in the higher 
plants and animals is not always* rounded spherical is 
due to unequal pressure and the movement of the cells 
comprising the body. 

The nucleus is a definite, clearly-marked body existing 
within the protoplasmic contents of the living cell, and 
its relation to growth, reproduction and heredity have 
given it a commanding position in the study of modern 
biological problems. Other bodies are often found in 
the cell, such as food granules, products of excretion, 
fat globules and crystals. None of these plays an active 
part in the metabolism of the cell and may be regarded 
as accidental or at least subsidiary to the major role 
played by the protoplasm itself. Another body generally 
found in the cell is the centrosome which is concerned 
with the mechanism of cell division. The cell-wall is 
generally present in the higher forms of plant and animal 
life and consists of a membrane which is usually lifeless. 

6. Protoplasm. — The protoplasm is universally present 
in every living cell. It is the most fundamentally impor- 
tant life substance. Huxley aptly designated protoplasm 
as " the pltysical basis of life." It is not to be regarded 



THE CELL ' 5 

as being a definite chemical substance, as its composition 
changes. It is a viscid, colorless, semifluid material 
having a higher index of refraction than water, and hence 
appears brighter. It was called slime by Schleiden. 
The protoplasm of the cell has a definite structural 
arrangement appearing as a meshwork, or reticulum, and 
a ground substance, or cell-sap, filling the intervening 
spaces. In addition to these two definite substances 
there are present in the protoplasm minute granules 
or microsomes which are distributed regularly or irregu- 
larly along the lines of the meshwork. While other 
materials are often found in the protoplasm, the above 
materials are regarded as the essential elements of pri- 
mary importance in the activities of the cell. 

7. The nucleus. — The nucleus is the center of the 
constructive activities of the cell. When the nucleus is 
destroyed, those processes which result in the growth 
and development of the organism can no longer take 
place. Only destructive activities are possible in a cell 
devoid of a nucleus, and these can go forward for only a 
limited time. " The nucleus is generally regarded," says 
Wilson, '' as a controlling center of cell activity, and hence 
a primary factor in growth, development and the trans- 
mission of specific qualities from cell to cell, and from 
one generation to another." ^ Growth is the result 
of cell division, and the impetus for cell division appears 
to come from the nucleus. The essential fact in cell 
division is that a portion of the nuclear material of the 
parent cell shall pass into the new cell. The new cell 
in its turn becomes a parent cell, and so the process of 
growth continues. The nucleus is typically spherical 
and moves freely within the cell. It exhibits two distinct 

1 Wilson, "The Cell in Development and Inheritance," p. 30. 



6 THE BREEDING OF ANIMALS 

phases which result from the varying degrees of activity 
present in the nuclear substance. One phase may be 
designated as the vegetative or quiescent stage and the 
other the active stage which is characteristic of that 
period in the development of the nucleus when the many 
complicated and significant changes occur which result 
in cell division and in reproduction. 

The typical nucleus during the vegetative stage pos- 
sesses certain distinct structural forms which are con- 
cerned in the many important nuclear activities: (1) 
The nuclear wall which encloses the nucleus and dif- 
ferentiates the nucleus from the cell-body; (2) The 
reticulum, which is the primary factor in nuclear activities, 
and appearing as an irregular network. The reticulum 
in turn comprises two structures, the linin and the chro- 
matin. The latter is undoubtedly the most fundamentally 
important organic substance concerned with the growth, 
development and inheritance of plants and animals. 
It is apparently the only or chief material which is trans- 
mitted from the parent cell to the new or daughter cell 
by division, and from it all nuclear substance may be re- 
formed. The word chromatin is given to this material 
because it becomes deeply stained upon the addition of 
certain well-known reagents. The chromatin may appear 
in the cell in scattered granules, varying in size and form, 
or in a single deeply staining mass, but more often the 
arrangement of the chromatin in the nucleus resembles 
a network which is closely associated with the clearly 
differentiated linin. (3) The nucleoli are generally but 
not always present, and their nature and functions are 
not well understood. By some authorities the nucleoli 
are the by-products of the activities going on in the 
nucleus. (4) The ground substance is a fluid filling 



THE CELL 7 

the chromatin network and is not stained by ordinary 
reagents. 

8. Growth by cell division. — How does growth take 
place in a living organism? What are the primary 
factors concerned in the increase in size? What changes 
in the organism result in the progressive development 
of the many useful qualities found in the improved types 
of the domestic animals? How does a microscopic egg- 
cell develop into a mature and highly organized animal 
possessing countless cells of many different forms and 
exercising various and important functions? A still 
more fundamental problem, if possible, is, how are the 
qualities of an individual transmitted from parent to 
offspring? What is the physical basis of heredity and 
what are the elements concerned in a study of inheritance ? 

Many of these questions are answered by a study of 
the cell and specifically by a study of cell division. The 
entire tissue structure of the animal body arises by re- 
peated division from the germ-cell. The germ-cell itself 
is the result of the division of a cell which formed 
a part of the body of the parent. Thus it is that the 
germ substance carrying the hereditary material is 
separated from the parent body by cell division. The 
fertilized egg by continued cell division passes on to every 
cell in the body a portion of its own substance. The 
process of cell division must therefore be regarded as a 
great fundamental fact in the growth and development 
of plants and animals as well as one of the most significant 
and primary facts in the transmission of qualities from 
parent to offspring. 

Growth occurs as the result of continued cell division 
rather than by any material increase in the size of exist- 
ing cells. 



8 THE BREEDING OF ANIMALS 

9. How cells divide. — All cells do not divide in the 
same manner, but the most typical process is known as 
indirect division or mitosis, and this will be here described. 
We have seen that the nucleus contains within its minute 
compass the active material which stimulates the cell 
to various activities and determines its physiological 
destiny. If further evidence was needed on this point, 
it would be found in the remarkable and interesting trans- 
formations which take place within the nucleus before 
and during the process of cell division. 

The cell first passes through a vegetative or quiescent 
stage, and this is followed by a period of activity finally 
resulting in the formation of two cells from the original 
parent cell. Various clearly marked stages or phases 
are distinguishable in this process which have been accu- 
rately described by Wilson. The phases observed are 
for convenience named : (1) prophase, (2) metaphase, 
(3) anaphase, and (4) telophase. 

10. Prophase (Fig. 1). — In the vegetative stage the 
chromatin of the nucleus exists in the form of a network. 
Generally during the prophase the chromatin loses its 
net-like arrangement and assumes the form of a skein 
like thread known as the spireme. During this stage 
the spireme thread stains intensely and is fine and closely 
convoluted. It gradually becomes thicker and the con- 
volutions become more open, giving rise to the '' open 
spireme." Gradually the spireme breaks up into a num- 
ber of definite straight or curved rods known as chromo- 
somes. It is usual for the wall of the nucleus to disappear 
during this phase, and the chromosomes then lie naked 
in the protoplasm of the cell. It is a significant fact that 
every plant and animal possesses a characteristic number 
of chromosomes and that this number is always even. 









Fig. 1. — Cell division. Diagram showing typical prophases in cell 
division. A, Vegetative or resting stage showing nucleus. B, The 
spireme thread. C, Preparation for division. D, Formation of chro- 
mosomes. E, Gradual fading of nuclear membrane. F, Chromosomes 
in equatorial plate ready for division. 

9 



10 THE BREEDING OF ANIMALS 

In the ox and in man the number is sixteen. The fact 
that the number of chromosomes is even in all species is 
due to the fact that during the processes of fertilization 
one-half the chromosomes are derived from the female 
and one-half from the male parent. 

After the breaking up of the spireme thread into a 
definite number of chromosomes, there is formed in the 
cell the so-called amphiaster. The development and 
activities of this interesting structure seem to be for the 
purpose of arranging the chromosomes in position for 
division. All the processes concerned in the prophases 
are preparatory to the final division, and ultimate dis- 
tribution of chromatin to the new cell. 

11. Metaphase. — Each chromosome now splits into 
two exactly equal halves and the two new groups move 
to opposite sides of the cell. The chromosomes divide 
lengthwise, and by so doing there results an accurate 
division of the chromatin into two precisely equivalent 
portions. Each portion eventually becomes the nucleus 
of one of the two new daughter cells which result from 
this division. The most fundamentally important fact 
about this division of the chromatin is that it is a qualita- 
tive as well as a quantitative division. There is much evi- 
dence to show that the spireme thread (and, therefore, 
the chromosomes) is composed of granules or units 
throughout its length, and each of these units represent^ 
a definite character or set of characters in the individual. 
It follows that when a lengthwise division occurs, these 
units are divided and a portion of each is passed on to the 
daughter cells (Fig. 2). 

The arrangement of the chromatin in the spireme, its 
breaking up into chromosomes, and the splitting of the 
latter into halves are all directed toward the accurate 



THE CELL 



11 







Fig. 2. — Diagram of later phases of cell division. G, Splitting of 
the chromosomes. H, Daughter chromosomes diverging to form new 
cells. 7, Chromosomes grouped in daughter nuclei, final changes before 
complete division. /, The two new cells. 



division of the smaller chromatin granule (chromo- 
mere or id as designated by Weismann). In this process, 
therefore, we have a reasonable physical basis for a better 
understanding of the transmission of characters from 



12 THE BREEDING OF ANIMALS 

parent cell to daughter cell and thus from parent to off- 
spring. 

12. Anaphase. — The essential step in the anaphase 
is the separation of the two groups of chromosomes which 
were derived from the splitting of the chromosomes of 
the parent cell. These pass to opposite sides of the cell, 
and in many forms these new groups begin at once to 
assume the appearance of the original nuclear material. 

13. Telophase. — Complete division of the cell is 
finally accomplished by constriction of the parent cell- 
walls and the formation of a new membrane w^hich encloses 
the two daughter nuclei each in its own cell. The two 
groups of chromosomes derived from the parent nucleus 
are rearranged and become the nuclei of the new daughter 
cells which in their turn may pass through all the stages 
described above. 

The essential steps, then, in cell division are : (1) The 
formation of the spireme thread from the chromatin 
and its division into chromosomes; (2) The splitting of 
the chromosomes through the middle longitudinally; 
(3) The movement of the divided portions of the chromo- 
somes to the new or daughter cells. 

14. The germ-cells in detail. — In all the higher forms 
of animals, reproduction is accomplished by the forma- 
tion of special reproductive cells called the germ-cells. 
The germ-cells are the product of the reproductive group 
of cells and are endowed with peculiar powers not gen- 
erally possessed by the soma- or body-cells. Weismann 
divided the cells of the body into two very clearly marked 
and distinct groups, the soma- or body-cells and the germ- 
cells. The soma-cells are primarily concerned with the 
individual life of the animal, while the germ-cells are 
destined solely for the purpose of reproduction. The 



THE CELL 



13 



germ-cells have no important relation to the functional 
activities which are especially concerned with the indi- 
vidual existence of the animal. They are clearly in- 
tended for ultimate separation from the individual and 
destined to provide for the continuance of the species. 
In some lower forms of life, the body-cells and germ-cells 
are not so clearly separated, but in the domestic animals 
such differentiation is characteristic. The male germ-cell 
is called the spermatozoon or sperm-cell, and the female 
germ-cell the egg or ovum. 

15. The ovum. — The germ-cell of the female is the 
egg or ovum (Fig. 3). It is one of the largest cells in the 
animal body. It is spheroidal in 
shape and contains a nucleus or 
germinal vesicle and within the 
nucleus a nucleolus or germinal 
spot and a large amount of pro- 
toplasm (cytoplasm) surrounding 
the nucleus. In the protoplasm 
are often distributed numerous 
masses of material or yolk, the 
function of which seems to be 
chiefly to nourish the fertilized 
egg-cell. The nucleus of the 
ovum during the quiescent stage lies near the center of 
the cell, but gradually moves toward the cell-wall as the 
egg becomes more mature. During the final stages in the 
development of the egg, the nucleus loses a large part of 
its chromatin. This process is called maturation and re- 
sults ultimately in reducing the number of chromosomes to 
one-half the number characteristic of the species. This 
process is preparatory to the fertilization of the egg by 
the spermatozoon. During fertilization, the chromo- 







'^ 



^m 



Fig. 3. — The 

egg. A, nucleus ; 
plasm. 



ovarian 
B, cyto- 



14 



THE BREEDING OF ANIMALS 



somes of the egg-cell unite with those of the sperm-cell 
and a new nucleus is thus formed which becomes the 
active center of the new daughter cell. 

16. The spermatozoon. — The male germ-cell or sper- 
matozoon is exceedingly minute and its investigation cor- 




FiG. 4. — Human spermatozoa (greatly magnified), a, acrosome; 
h, nucleus ; c, end knob ; d, middle piece ; e, tail ; /, end piece ; g, axial 
filament. 

respondingly difficult. Although early discovered, its 
significance was not clearly determined until 1865 when 
Schweigger-Seidel and St. George discovered that the 
sperm was a cell and contained a nucleus, cytoplasm and 
all the essential elements of a perfect cell. The function 
of the sperm-cell is to fertilize the egg and thus provide 



THE CELL 15 

for the reproduction of the species. The spermatozoon 
in its gross anatomy has the semblance of a very minute 
tadpole swimming freely about in liquids. It has a 
distinct head piece and a long slender tail piece or cilium. 
(See Fig. 4.) When closely examined, the sperm-cell 
exhibits all the essential characteristics of a typical cell, 
'with a nucleus, cytoplasm and a cell-wall. This cell is 
so small that in some forms it is but i o oVo o ' of the size 
of the egg-cell. The nucleus occupies almost the entire 
space available in the head piece, being surrounded by 
a very thin layer of cytoplasm between it and the cell- 
wall. The tail of the sperm-cell is joined to the head 
piece by the middle piece. It is of cytoplasmic origin 
and possesses the power of motion. This ability to propel 
itself forward in liquid media seems to be in a way an 
insurance that the sperm-cell will ultimately approach 
the egg-cell for the purpose of fertilization. 

The power of motion is retained by the spermatozoon 
for a considerable time under favorable conditions of 
warmth and moisture. After the sperm enters the egg, 
it loses the power of motion and the tail piece is absorbed. 

The essential portions of the sperm which are concerned 
in the process of fertilization are the nucleus and the 
middle piece. Other structures which are accessory to 
these are the apex by which the sperm attaches itself 
to the ovum and the tail whose functions have already 
been described. 



CHAPTER II 
REPRODUCTION 

The value of a breeding animal is measured by its 
own individual character, its ability to transmit desir- 
able characters to its offspring, and by its prolificacy. Of 
two animals of equal individuality and inheritance, the 
one capable of producing numerous and vigorous offspring 
will be the more valuable. The subject of reproduction 
in animal-breeding is therefore of great importance and 
second only to inheritance in estimating animal values. 

Two methods of reproduction are common among 
plants and animals, asexual and sexual. These differ 
greatly in form and method but accomplish the same 
ultimate result, which is the continuance of the race. 

17. Asexual reproduction. — The asexual method of 
reproduction is common among the simplest forms of 
plant and animal life. It is a process of cell division 
or fission which varies in different forms, but in its most 
elementary manifestations it is simple cell division. In 
unicellular forms the cytoplasm of the cell and the nucleus 
divide into two equal parts and each half becomes a 
perfect new individual. Each new cell increases in bulk 
by the absorption of food and in turn becomes a parent 
cell and reproduces by division as before. A similar 
form of reproduction is found in the developing embryo 
of mammals and of the other body-cells. The tissues of 

16 



REPRODUCTION 17 

the body thus formed cannot, however, continue to divide 
indefinitely, but sooner or later reach their full develop- 
ment and do not thereafter increase in bulk by further 
division. 

18. Sexual reproduction. — Reproduction in the higher 
forms of organic life is a complicated process and is ac- 
complished by the activities of a special group of cells 
which is called the reproductive or generative system. 
These germ-cells are highly specialized, and their develop- 
ment and functions divide the individuals of a species 
into two sexes, male and female. The two sexes differ 
widely in form and characters, but particularly in respect 
to their physiological relations to reproduction. The 
product of the male. germ-cells is the spermatozoon, an 
exceedingly small cell but carrying in its minute substance 
the inherited potentialities of its ancestors. The female 
germ-cell or ovum similarly derived from the female is 
much larger, but also carries the germ substance which 
later, after fertilization by the spermatozoon and under 
proper conditions, will become a new individual. 

19. The reproductive process. — The essential fact 
in the reproductive processes of all vertebrate animals 
is the formation of an egg or ovum by the female and of a 
fecundating fluid containing the spermatozoon or sperm- 
cell by the male. The union of the two germ-cells is the 
first step in the independent existence of the new indi- 
vidual. The conjugation of the egg and spermatozoon 
sets in motion a series of events which, whether viewed 
from the standpoint of racial significance or of biological 
interest, has no parallel in the whole realm of biology. 
Upon the successful development of the fertilized egg- 
cell depends the future of the species. The union of the 
egg and spermatozoon takes place in some forms outside 



18 THE BREEDING OF ANIMALS 

the body of the female. In fishes, the spawn con- 
taining the eggs is deposited in the water by the female, 
and the fertilizing fluid of the male containing the sper- 
matozoa is also deposited in the water on or near the female 
spawn. In all higher animals, including the domestic 
animals, the fecundating fluid of the male reaches the 
egg inside the body of the female, and the process of ferti- 
lizing the egg is accomplished within the generative organs 
of the female. 

20. Oviparous animals. — In some species of animals, 
including birds, fishes, most reptiles, and nearly all 
invertebrates, the eggs are deposited outside the body 
either before or after fertilization. In the bird family, 
which includes all the domestic fowls, the egg is fertilized 
inside the body of the mother, where it undergoes some 
slight development before being eventually deposited or 
laid outside the body of the female. Animals of this 
class are called oviparous, to distinguish them from vivip- 
arous forms which bring forth their young alive. The 
future development of the egg deposited by oviparous 
animals is dependent upon its being supplied with favor- 
able conditions of heat and moisture. This period of 
development outside the body is called the period of 
incubation and is, in many ways, similar to the period 
of gestation in viviparous animals. Animals in which 
the fertilized egg develops inside the body are called vivip- 
arous, and this development proceeds to a point where 
the young animal is, in the main, able to carry on a sepa- 
rate and independent existence. The period of growth 
inside the body of the mother in mammalian animals is 
called the period of gestation, and during this period 
the developing embryo is gradually fitted for an inde- 
pendent life outside the protecting body of the mother. 



REPRODUCTION 19 

21. Primary and secondary sexual characters. — 

The particular characteristics which differentiate the 
male from the female sex may be divided into primary 
and secondary characters. The primary characters are 
those which are peculiar to the sex. In the male, the 
form and functions of the generative organs clearly 
differentiate him from the female. As Lee ^ has pointed 
out, the function of the primary sexual characters of 
the male is the production of spermatozoa and the im- 
pregnation of the female Qgg. The activities of the 
primary sexual organs of the female center about the 
production of the egg and the development of the 
embryo. 

The secondary sexual characters are those which may 
often be possessed in common by both sexes but experi- 
ence a special and somewhat different development in 
the two sexes. Examples of secondary sexual characters 
are the horns of the ram in some breeds of sheep, the 
spurs of the cock, the tusks of the boar, the various col- 
ored plumage of many male birds, and the crest in stal- 
lions and bulls. Under certain conditions, the secondary 
sexual characters which are in general characteristic of 
the male sex alone may be developed in the female. Thus, 
hens sometimes develop spurs and ewes develop horns. 

Castration of the male causes a check in the develop- 
ment of the secondary sexual characters and causes the 
male to approach more nearly to the form and appear- 
ance of the female. 

22. The reproductive organs of the male (Fig. 5). — The 
organs of generation in the male are : (a) the testicles, cor- 
responding to the ovaries in the female ; {h) vasa def erentia, 
or the ducts leading from the testicles to the ejaculatory 

1 "American Text Book of Physiology," 1903, p. 443. 



20 THE BREEDING OF ANIMALS 

duct; (c) vesiculse seminales; {d) prostate glands; {e) 
Cowper's gland ; (/) urethra*, through which the urinary 
and genital secretions are conveyed ; {g) the penis, 
through which the semen of the male is conveyed to the 
female genital organs. The secretions of the vesiculse 
seminales, the prostate, and the Cowper's gland all empty 
into the urethra, where they mix with the seminal fluid 
from the testicles. The testicles, vasa deferent ia and 
urethra and penis are often called the essential organs of 
generation, while the remaining three are referred to as 
the accessory organs. 

23. The testicles. — The essential sexual elements, 
the spermatozoa, are formed in the testicles. The removal 
of the testicles, therefore, destroys the ability of a male 
animal to elaborate the male germ-cells and permanently 
destroys his fecundity. The structure of the testis is 
described in some detail by Marshall as follows : ^ '' This 
organ is enclosed within a fibrous capsule, the tunica 
albuginea, which is very rich in lymphatics. It is cov- 
ered by a layer of serous epithelium reflected from the 
tunica vaginalis. Posteriorly the capsule is prolonged 
into the interior of the testis in the form of a mass of 
fibrous tissue (the mediastinum testis). Certain other 
fibrous processes or trabeculse also project inwards from 
the capsule, and divide the glandular substance into 
lobules. The efi^erent ducts of the testis (vasa efferentia) 
open into a single convoluted tube situated at the pos- 
terior margin of the organ and attached to the medias- 
tinum. This is the epididymis. Its lower extremity 
is prolonged into a thick-walled muscular tube (the vas 
deferens) which is the passage of exit for the seminal 
fluid or sperm-containing secretion. The glandular sub- 

1 Marshall, "The Physiology of Reproduction." 



REPRODUCTION 



21 




Fig. 5. -Genital organs of boar, l^testlcle; 2 epididymis 3, 
vas deferens; 4, spermatic artery; 5, vesicula semmalis; 6 prostate 
7 Cowper's gland; 8, bulbo cavernosas muscle; 9, 9 and 9 , penis, 
10, retractor penis muscle; 12, orifice of preputial pouch. 



22 THE BREEDING OF ANIMALS 

stance of the testis is composed of the convohited seminif- 
erous tubules, two or three of which join together to 
form a straight tubule which passes into the body of 
the mediastinum. The straight tubules within the 
mediastinum unite in their turn, giving rise to a network 
of vessels called the rete testis. From the rete the vasa 
efferentia are given off. Between the tubules is a loose 
connective tissue containing a number of yellow epithelioid 
interstitial cells. The connective tissue also contains 
numerous lymphatics and blood-vessels (branches of the 
spermatic artery). The nerves of the testis are derived 
from the sympathetic system, but a few filaments come 
from the hypogastric plexus." 

The male reproductive organs ^ other than the testicles 
are chiefly concerned in providing for the transmission of 
the fully mature sperm-cells from the testicles. The 
seminal fluid is secreted by the seminiferous tubules and 
after expulsion is mixed with other fluids from the male 
accessory organs. 

The function of the seminal fluid seems to be to pro- 
vide a favorable medium for the spermatozoa. 

24. Castration. — The removal of the testicles of the 
male results in profoundly influencing not only the breed- 
ing function of the animal but in marked bodily change. 
While the testicles seem to have no important connec- 
tion with or relation to the body-cells and their removal 
interferes in no way with the normal, healthy function- 
ing of the other bodily organs, it is nevertheless true that 
castration materially influences the animal economy. 

1 The student is referred to standard works on anatomy and 
physiology for a detailed discussion of the organization and 
functional relations of the various male reproductive organs. 
See Sisson, "Veterinary Anatomy." 

Chauveau, "Veterinary Anatomy." 



REPRODUCTION 23 

If the young male is castrated, the external appearance 
of the animal undergoes a gradual change. The whole 
aspect becomes less masculine. The shoulders, neck 
and crest develop relatively to a much less extent. The 
hind quarters are relatively better developed in the 
cas|rated animal. The temperament and disposition 
undergo radical changes. The bull castrated before 
puberty fails to develop the heavy head and horns, curly 
hair and protruding eye characteristic of this animal. In 
swine, castration prevents the development of the shoulder 
plates and tusks. The horns of sheep are very greatly 
dwarfed, though the same effect is not so marked in cattle. 
The removal of the testicles also influences the physiolog- 
ical constitution of the animal. It is well known that 
oxen grow larger and heavier than the uncastrated bulls. 
The same result is observed in capons which often grow 
to a much greater weight than the normal male. The 
castration of old boars results in the disappearance of 
the strong odor characteristic of the flesh, and their food 
value is thereby increased. 

The removal of the ovaries (spaying) of the female 
is followed by phenomena similar to those observed in 
the castrated male. The spayed female loses her feminine 
appearance and approaches the male in general char- 
acter. Like the male, the disposition becomes quieter 
and the general physiological condition of the animal 
favors more rapid laying on of fat. 

At the Massachusetts Experiment Station, Goodale ^ 
castrated a brown Leghorn cockerel at twenty-four days 
old. At the same time the fresh ovaries of two brood 
sisters were cut in several pieces and placed under the 
skin of the castrated cockerel. The bird developed in 

1 Goodale, ** Science," Vol. 40 (1914), p. 549. 



24 THE BREEDING OF ANIMALS 

every external character like a female, so much so that 
expert poultry men were deceived. 

We may conclude that the castration of animals is 
successful in preventing undesirable animals from re- 
producing, improving the fattening qualities of the meat 
animals, increasing the size in some cases, improving 
the quality of the flesh, and increasing the value of draft 
animals.^ 

25. The reproductive organs of the female (Plate II). — 
The essential organs of reproduction in the female are 
the two ovaries. The accessory organs are the Fallopian 
tubes, the uterus, the vagina, the vulva and the mammary 
glands. The function of the female organs of generation 
is the production of the female germ-cells or ova and, 
when fertilized, to provide nutrition and proper support 
for the developing embryo. 

26. The ovaries. — The female egg has its origin in 
the ovary. This organ is composed of connective tissue, 
blood-vessels, nerves and lymphatics enclosed in an outer 
covering — the epithelium. A cross-section of the ovary 
of any mature breeding animal will exhibit a large number 
of follicles or sacs scattered through its vascular substance 
(Fig. 6). The latter are small, varying from one-hundredth 
to one-thirtieth of an inch in size.^ These small sacs are 
called the Graafian follicles, and each contains an ovum 
or egg. The eggs or ova in these follicles exhibit various 
stages of development, some being almost or quite mature, 
while others are very small and undeveloped. The 
beginning of the formation of a Graafian follicle is indi- 
cated by a slight depression in the surface of the ovary 
which gradually extends into the substance of the ovarian 

1 Pusch, "AUegemeine Tierzucht," 1911, p. 153. 

2 Smith, "Physiology of the Domestic Animals," p. 909. 




REPRODUCTION 25 

tissue in the form of a tubule. Eventually this sac 
becomes constricted at the surface of the ovary until 
finally the external opening is entirely closed and the 
tubule becomes a closed follicle within the tissues of the 
organ. Within the follicle 
itself, there have been 
formed, in the meantime, 
single, large spherical cells 
(primordial germ-cells) 
from which one or some- 
times two ova are devel- .0-~^-:k 
oped. The part of the t^^^ 

Graafian follicle not OCCU- ^ig. 6. — Sections through ovary 

pied by the ovum is filled of rat, typical of ovarian structure in 
• ,i n 'A u X mammals. 

With a nuid substance. 

The follicle increases in size and approaches the center of 
the ovary until near maturity, when it rises to the surface 
and finally is ruptured, thus liberating the enclosed egg. 
The bursting of a Graafian follicle and the discharge 
of the egg is called ovulation. This event is marked 
by certain phenomena indicating increased sexual activity. 
It is believed that menstruation or the period of heat in 
domestic animals is coextensive with the ripening of 
the egg. It is true, however, that, under some circum- 
stances, ovulation may occur before or after the period 
of heat. The ripening of the first Graafian follicle in 
general marks the beginning of. puberty, but has been 
known to occur even in infancy. In animals generally 
ovulation does not occur during pregnancy, but there 
are numerous exceptions to this rule, as will be described 
later in the case of some animals which have come in heat 
and have even conceived again, although pregnant at 
the time (Fig. 7). 



26 



THE BREEDING OF ANIMALS 




Fig. 7. — Genital organs of mare. 1, ovary ; 2, Fallopian tube ; 2', 
fimbriated end of Fallopian tube ; 3, uterus ; 5, horn of uterus ; 6 and 
6',^ cervix ; 7, broad ligament of uterus ; 9, vagina ; 10, vulva ; 13 and 
13', lips of vulva; 14, clitoris; 15, urinary bladder; a, utero-ovarian 
artery with branches to ovary (a) and uterus (a") ; 6, uterine artery. 



REPRODUCTION 27 

Some of the domestic animals do not come in heat 
while suckling young, while others discharge eggs and 
undergo the periodical phenomenon of heat as readily 
during lactation as at any other time. 

27. The Fallopian tubes. — The egg which has been 
discharged as the result of the processes described above 
finds its way to the uterus through the Fallopian tubes 
in mammals or the oviduct in birds. These are small, 
very crooked canals leading from the ovary to the uterus. 
This accessory organ is not rigidly joined to the ovary 
by tissues, but the end nearest the ovary is mostly free 
to move to different sides of the ovary. The ovarian 
end of the Fallopian tube is expanded into a fimbriated 
extension which spreads out not unlike the fingers of the 
hand. The comparison will be still more exact if we con- 
ceive of the fingers of the hand as being connected by 
web-like tissues. 

In many mammals, the tube is lined with cilia which 
move from the ovary toward the uterus. In normal 
cases when the egg is discharged from the ovary, the 
fimbriated expansion of the Fallopian tube clasps the 
ovary at the point where the Graafian follicle bursts 
through its walls. The ciliary movement within the tube, 
assisted by muscular movements of the tube itself, carries 
the egg from the ovary to the uterus. The time required 
for the passage of the egg through the Fallopian tube has 
not been definitely determined for all mammals, but is 
known to vary from three to eight days. 

The union of the spermatozoon and the egg usually 
takes place in the Fallopian tube. To accomplish this 
union, it is necessary for the sperm-cell to pass into the 
uterus and up into the tube. This it is able to do by 
reason of its possessing the power of independent motion. 



28 THE BREEDING OF ANIMALS 

28. The uterus. — The uterus is a muscular sac con- 
necting the Fallopian tubes and the vagina in which the 
development of the fertilized egg is carried forward until 
expelled from the body of the mother at the time of par- 
turition (Figs. 8, 9, 10). 

In many mammals the uterus divides into two tubes 
called horns. Each horn is connected with the corre- 
sponding ovary by means of the Fallopian tube. 

The portion of the uterus nearest the vagina is some- 
what constricted to form the cervix or neck of the uterus. 
The vagina connects the uterus with the external genitals 
called the vulva. 

29. The mammary glands. — The possession of mam- 
mary glands whose function is the elaboration of food 
materials for the young offspring is characteristic of 
all mammals. These glands are highly developed and 
functional in the fertile female, but are also present in 
rudimentary form in the male. In rare cases the rudi- 
mentary glands present in the male have been known 
to function. Hayward at the Delaware Experiment 
Station reports the case of a registered Guernsey bull 
owned by that institution whose mammary glands 
were developed to the extent of producing a small 
amount of milk. Milk has also been produced from 
the rudimentary mammary glands of male goats and 
sheep. In man the rudimentaries of males have pro- 
duced milk at birth and at puberty and in exceptional 
cases at other times. The number of nipples in a 
species bears some relation to the normal number of 
young produced in a litter, and also to the needs of 
the young animal. The glands are generally arranged 
in pairs either along the ventral side of the thorax or 
abdomen. 



30 



THE BREEDING OF ANIMALS 




Fig, 9, — Genital organs of the sow. 1, lips of vulva ; 2, clitoris ; 
3, vulva ; 4, external opening of urethra ; 5, vagina ; 5, cervix ; 6, body of 
uterus ; 7, horn of uterus ; 7', horn of uterus opened to show interior ; 
8, Fallopian tube ; 8', abdominal opening of Fallopian tube ; 9, ovaries ; 
12, urinary bladder. 



REPRODUCTION 31 

30. Structure of mammary glands.^ — The mammary 
glands are made up of lobes which in turn are further 
divided into lobules. The latter arise from secretory 
alveoli. The lobule is chiefly connective tissue binding 
together the milk ducts. The alveoli unite together 
to form the lactiferous ducts which open externally. 
These ducts are provided with reservoirs w^herein the 
milk is accumulated during the period of active lac- 
tation. During lactation the alveoli secrete milk. This 
secretion goes forward at all times, but is particularly 
active during suckling. The milk drawn first is of 
poorer composition in respect to solids than that drawn 
near the end of the milking. This may be due to the 
fact that the larger globules pass through the ducts 
with greater difficulty and are thus retained longer in 
the gland. 

The processes concerned in milk secretion are not 
entirely understood, at least three views having been 
held. One hypothesis is that the secretory cells them- 
selves break down and thus set free their contents as is the 
case with the sebaceous glands. Another view^ is that 
the milk is simply excreted from the cell without causing 
the breaking down of the cell, in a manner similar to 
that which occurs in many secretory glands. 

" The third theory ^ was first suggested by Langer, 
and has since been adopted, with various slight modifi- 
cations, by Heidenhain, Steinhaus, Brouha and others. 
According to their view the cells of the gland lengthen 
out, so that their ends come to project freely into 
the lumina of the alveoli. The projecting portions 
then undergo a process of disintegration before or after 

1 Marshall, "The Physiology of Reproduction," p. 553. 

2 lUd., p. 560. 




c 



Fig. 10.— Genital 
organs of bitch, a, 
ovarian bursa ; b, 
opened to show ova- 
ry ; c, ovary ; d, d, 
horns of uterus ; e, e', 
body of uterus ; /, 
neck of uterus; /', 
cervix (os uteri) ; g, 
vagina ; i, vulva ; k, 
opening of urethra ; 
I, urinary bladder ; 
m, urethra ; n, n, lips 
of vulva ; p, clitoris. 
Vulva, vagina and 
uterus cut open to 
show interior. 



2" 
32 



REPRODUCTION 33 

becoming detached, and the cell substance passes into 
solution to form the albuminous and carbohydrate con- 
stituents of the milk. The fat droplets which collect in 
the disintegrating part of the cell give rise to the milk 
fat. The basal portions of the cell remain in position 
without being detached, and subsequently develop fresh 
processes, which in their turn become disintegrated. It 
is believed, however, that some cells simply discharge 
their fat droplets and other contents into the lumina, 
while otherwise remaining intact." 

31. Fertilization of the ovum. — We have seen how 
growth may continue for a long period by successive 
cell division. Indeed, in many of the simpler forms, 
Wilson has pointed out that " as far as we can see from 
an a 'priori point of view, there is no reason why, barring 
accident, cell division should not follow cell division in 
endless succession in the stream of life." ^ 

In some of the very simplest forms, no sexual union 
has so far been discovered. But, under normal conditions, 
reproduction without sexual union is rare and practically 
unknown in the higher animals. The impetus to growth 
and cell division is not permanent and must be constantly 
renewed. The stimulus to renewed growth is accom- 
plished by the definite mixture of living protoplasm from 
two entirely distinct individuals. This process of fertili- 
zation involves a union of the ovum of the female and 
the spermatozoon of the male. This union is the begin- 
ning of the life of each individual and results not only 
in energizing the protoplasm of the germ-cell, causing it 
to divide and grow, but the admixture of germ material 
from two different individuals introduces into the new 
organism two distinct lines of inheritance. 

1 Wilson, "The Cell." 



34 THE BREEDING OF ANIMALS 

32. The nature of fertilization. — The essential na- 
ture of fertihzation still remains a matter of discussion. 
It may be that the fertilization of the egg is primarily 
a rejuvenescence of the protoplasmic material which, for 
some at present unknown reason, has lost the power of 
further growth through cell division. This view was 
held by Butschli, Hertwig, Minot, Engelman and others. 
Even in the simpler forms of life where anything like 
sexual union is absent, the cycle of growth is continually 
reinaugurated by the conjugation of independent cells. 
In all higher forms the egg is stimulated to growth and 
cell division by the introduction of the sperm. 

Weismann has looked upon fertilization as a source 
of variation and has maintained that this should be 
regarded as the chief function of this process. Both 
the theory of rejuvenescence and that which regards 
this process as chiefly a source of variation are in accord- 
ance with the observations of practical breeders. Cross- 
breeding is known to induce greater vigor and increased 
fecundity and at the same time to break up the fixed 
characters of the breed or type. It is equally well estab- 
lished that under certain conditions in-breeding tends to 
identity of character and results in sterility and weakness 
of constitution. But, after all, the real purpose and na- 
ture of sexual union in reproduction is still an unsolved 
problem. 

33. The process of fertilization. — The ultimate pur- 
pose of the sexual union of animals is to insure the fertili- 
zation of the egg by the spermatozoon. When the egg 
and sperm meet within the generative organs of the fe- 
male, significant and important changes are set in motion, 
which eventually result in an admixture or union of the 
germ substance of the two parents. These changes are 



REPRODUCTION 35 

primarily concerned with the nuclei of the egg and the 
sperm. 

In most species of animals, there is a definite attrac- 
tion existing between the egg and the sperm-cell, which 
causes the spermatozoon to attach itself to and finally 
penetrate the egg. This attraction is probably of a 
chemical nature. Pfeffer found that solutions of malic 
acid were as successful in attracting the sperm-cells of 
ferns as the substance which was thrown off by the female 
sex cells. In other experiments, other chemical sub- 
stances have exhibited a specific attraction for the sperm. 
The seat of this chemical substance which pulls the 
sperm to the egg seems to be located in the cytoplasm of 
the egg and not in the nucleus. 

The point at which the spermatozoon enters the egg 
is often predetermined by the existence of a depression 
or opening (micropyle) in the wall of the ovum. In 
some cases, there exists a special protoplasmic attraction 
cone at which point the sperm enters the egg. The 
entrance of the sperm in most cases is followed rapidly 
by the formation of a vitelline membrane which surrounds 
the egg and prevents the entrance of other spermatozoa. 

Normally in mammals one sperm only enters the egg. 
When through accident two or more spermatozoa enter 
the substance of the egg, the developmental changes are 
abnormal and the daughter nucleus soon dies. 

34. The chromosomes. — When the germ nuclei unite 
to form the daughter nucleus of the new cell, it seems 
probable now that the chromatin substance does not fuse 
in true fashion but the chromosomes may lie side by side 
within the nucleus of the new cell. It is not definitely 
determined that these chromosomes remain thus separate 
and apart throughout the life of the cell, but such may be 



36 THE BREEDING OF ANIMALS 

the case. After the reduction of the chromosomes in 
the maturation of the germ-cells and accompanying the 
formation of the polar bodies, the number of chromosomes 
is reduced to one-half the number existing in the body- 
cells and these uniting with an equal number from the 
sperm constitute the normal number characteristic of 
the tissue cells. As Wilson says, " We have thus what 
must be reckoned as more than a possibility that every 
cell in the body of the child may receive from each parent 
not only half of its chromatin substance, but one-half 
of its chromosomes, as distinct and individual descendants 
of those parents." 

35. Results of union of egg and sperm. — Extraor- 
dinary changes follow immediately the physical union 
of the egg and spermatozoon. These changes are of 
the most fundamental significance in connection with 
discussions of development and inheritance. 

36. Changes in the ovum. — The entrance of the 
sperm seems to exert an influence which permeates the 
entire constitution of the egg substance. Various and 
important changes now take place, ending finally in an 
exact union of the germ substance of the two sex cells, 
thus forming the new or daughter cell. The daughter 
cell is the beginning of a new individual and becomes the 
offspring of the parents, from which the sperm and ovum 
were derived. When the sperm enters the egg, the 
vitelline membrane is thrown around the outside of the 
ovum. The nucleus of the egg, which is now called the 
germinal vesicle, moves to the wall, and changes occur 
which result in the formation of the polar bodies. This 
process prepares the germ nucleus of the egg for ferti- 
lization. 

The polar bodies are formed by successive divisions 



REPRODUCTION 37 

of the egg nucleus. During their formation, the number 
of chromosomes characteristic of the species is reduced 
by half, so that when the egg nucleus is finally ready for 
union with the sperm nucleus, it contains exactly one-half 
the number of chromosomes usually present in the cell. 
There are formed in all three polar bodies. The divisions 
which occur in their formation separate the mass of 
chromatin originally present in the germinal vesicle 
into four equal parts. One-fourth part enters the egg 
nucleus and the other three parts are distributed, one to 
each of the polar bodies. The polar bodies are in no 
direct way concerned in fertilization and soon disinte- 
grate and disappear. 

37. Changes in the spermatozoon. — After contact 
with the egg, the tail of the sperm soon degenerates 
either outside or, in some cases, inside the egg. 

The nucleus of the sperm grows rapidly in size. The 
nucleus is further stimulated to cell division by the 
influence of the cytoplasm of the egg. 

38. The significance of reduction. — All the phenom- 
ena attending the processes of fertilization seem to 
have been specifically arranged for the purpose of bringing 
about a reduction of the number of chromosomes in the 
germ-cells to one-half that found in the other cells of the 
body. A result so universal in plants and animals must 
possess some significance in the reproduction of living 
forms. This change is characteristic of the germ-cells 
only and always occurs prior to and in preparation for 
the union of the spermatozoon and the egg. What is 
the real significance of the reduction of the chromosomes ? 
Is this reduction of the chromatin a quantitative one, or 
is it in some way a qualitative division? It must be 
admitted that we cannot yet give positive answers to 



38 THE BREEDING OF ANIMALS 

these questions. That this process is one of fundamental 
significance and is intimately connected with the problem 
of how characters are transmitted, is certain. Mani- 
festly its purpose is to provide for a constant number of 
chromosomes in the body tissues. It is not, as some have 
maintained, a mere mass reduction of the chromatin. 
Weismann's ingenious theory of the germ-plasm attempts 
to explain the process and to point out the hereditary 
significance of reduction. In an earlier investigation, 
Roux held that the hereditary qualities are represented 
by the individual chromatin granules. During cell di- 
vision, these arranged themselves side by side in the 
spireme thread, and the splitting of the spireme thread 
longitudinally actually resulted in halving each indi- 
vidual chromatin granule. Quoting Wilson,^ — " Roux 
assumes, as a fundamental postulate, that division of the 
granules may be either quantitative or qualitative. In 
the first mode, the group of qualities represented in the 
mother granule is first doubled and then split into equiva- 
lent daughter groups, the daughter cells, therefore, receiv- 
ing the same qualities and remaining of the same nature. 
In ' qualitative division,' on the other hand, the mother 
group of qualities is split into dissimilar groups, which, 
passing into the respective daughter nuclei, lead to a 
corresponding differentiation in the daughter cells. By 
qualitative divisions, occurring in a fixed and predeter- 
mined order, the idioplasm is thus split up during ontogeny 
into its constituent qualities which are, as it were, sifted 
apart and distributed to the various nuclei of the embryo. 
Every cell nucleus, therefore, receives a specific form of 
chromatin which determines the nature of the cell at a 
given period in its later history. Every cell is thus 

1 Loc. cit. 



REPRODUCTION 39 

endowed with a power of self-determination which Kes 
in the specific structure of its nucleus, and its course of 
development is only in a minor degree capable of modi- 
fication through the relation of the cell to its fellows." 

Weismann conceives that the chromatin (idioplasm) 
of the germ-cell exists in the form of minute particles 
which combine to form aggregates, and these again unite 
to form compound groups and so on until finally we have 
the chromosomes. He calls the smallest groups deter- 
minants, the next larger groups ids (chromatin granules), 
these in turn combining and forming idants or chro- 
mosomes. Weismann in explanation of his theory says : 
" Ontogeny depends on a gradual process of disintegra- 
tion of the id of germ-plasm, which splits into smaller 
and smaller groups of determinants in the development 
of each individual. Finally . . . only one kind of 
determinant remains in each cell, viz. that which has to 
control that particular cell or group of cells. In this 
cell it breaks up into its constituent biophores and gives 
the cell its inherited specific character." 

In developing this theory it is necessary to assume a 
very stable condition of the germ-plasm. For example, 
one must assume that some portion of the original germ- 
plasm is passed on to the germ nucleus unchanged in 
structure from generation to generation. 

The theories of both Roux and Weismann are in part 
only based upon demonstrated phenomena occurring in 
the cell. Some of the most fundamental and far-reaching 
postulates of these theories are highly speculative and 
cannot be demonstrated by any known method of re- 
search. It must be admitted, however, that Weismann's 
theory of the germ-plasm with some modifications comes 
nearer to an adequate explanation of the changes which 



40 THE BREEDING OF ANIMALS 

can actually be observed in the cell during the fertiliza- 
tion and maturation of the germ-cells than any other so 
far advanced. 

39. The origin of the germ-cells. — The origin of the 
germ-cells and the phenomena attending the process of 
the reduction of the chromosomes are of great fundamental 
significance. The functions of the chromatin in modern 
theories of heredity, the particular meaning of the pro- 
cesses which result in reducing the number of chromosomes 
to one-half that found in the body-cells, are problems 
of the greatest interest in modern biology. 

The maturation of the germ-cells is brought about 
by similar processes in the egg and sperm. The impor- 
tant result which is the reduction of the number of chro- 
mosomes is accomplished in each. This is brought about 
finally in the last two maturation divisions resulting in four 
cells, each of which contains but one-half the number of 
chromosomes characteristic of the same cells. In the 
female three of the four cells are the polar bodies which 
are abortive and disappear. The remaining cell is the 
ovum and becomes the carrier of the hereditary substance 
of the female. In the male the reduction divisions occur 
as in the female, but all four cells are functional and may 
take part in the process of fertilization. 

40. Maturation and reduction in the female (oogenesis) . 
— The female germ-cells are derived from the primordial 
germ-cells of the mother. Successive divisions of the 
primordial germ-cells result in the development of a 
number of cells known as oogonia. 

From these the ovarian eggs are directly derived. 
Their growth is characterized by an increase in the size 
of the nucleus which in the ovarian egg (oocyte) becomes 
the germinal vesicle. Food materials develop in the 



REPRODUCTION 41 

cytoplasm, which is now called the yolk. During all the 
changes described above, the number of chromosomes 
in the ova remains the same as in the body-cells. When 
the Qgg undergoes the final preparation for fertilization, 
as we have seen, the number of chromosomes is reduced 
by one-half. 

41. Reduction in the male (spermatogenesis). — The 
changes which bring about the reduction of the chromatin 
in the male germ-cell are almost exactly similar to those 
which have been described in the development of the 
ovarian egg. The spermatozoa originate in the primor- 
dial germ-cells. In their earlier development by cell 
division, numerous spermatogonia are formed which for 
a time continue to divide with the typical number of 
chromosomes found in the soma-cells. In time the 
spermatogonia cease to divide further and become larger. 
At this stage they are physiologically equivalent in func- 
tion to the oocyte of the female and are known as sperma- 
tocytes. There now occur two divisions resulting in four 
cells, each having but one-half the typical number of 
chromosomes. Unlike the reducing process in the female 
which results in only one perfect ovum and, three abortive 
cells, all four sperm-cells are functionally perfect. 

42. The period of the oestrum or heat. — In all the 
domestic mammals, the ripening of the first egg is asso- 
ciated with the first appearance of heat. It is the first 
evidence of puberty and is accompanied by the rapid 
development of all the secondary sexual characters dis- 
tinctive of sex. It is by no means certain that the stimu- 
lus which causes the heat or oestrum in animals originates 
in the ovary. It is possible that the stimulus to egg forma- 
tion is to be found in the influences set in motion by the 
oestrum itself. The production of ova ^nd the heat 



42 THE BREEDING OF ANIMALS 

period are so closely associated that the stimulus, what- 
ever it may be that causes the one, will probably under 
normal conditions directly or indirectly cause the other. 

Heape has maintained that since it is known that, 
in various animals, either menstruation or oestrus may 
take place without ovulation, and that ovulation may 
occur without the coincidence of menstruation (Leopold 
and Mironoff, 1894) or of oestrus (fat), the possibility of 
isolating these functions is demonstrated. Thus it is 
no longer impossible to suppose that, while they are 
both due to similar stimulating influences, one of them 
may be developed in excess of the other.^ 

It is probable that heat may sometimes occur with- 
out the production of an egg, and it is possible that the 
production of an egg may not always be accompanied by 
heat, but when such a condition exists, it is to be regarded 
as the exception and not the rule. It is very clear that 
the oestrum and ovulation are influenced by nutrition. 
An insufficient supply of food, deficient in the essential 
elements required for the normal development of animals, 
retards the first appearance of heat in young animals and 
causes irregular periods in mature animals. Breeders 
of live-stock have long known that the oestrum can 
be materially influenced by the method of feeding. 
Skillful stockmen feed the females in such a manner 
as to cause them to be " gaining " at mating time. This 
is accomplished by richer feeding or turning to fresh 
grass. 

43. Artificial insemination. — The transfer of the 
semen of the male to the uterus of the female by the aid 
of instruments or capsules is known as artificial insemina- 
tion or, more commonly among practical breeders, as 

^ Heape, loc. cit., p. 34. 




O •- f-i •- 

... cJ « j5 *s 



> > 73 -S 
2 t-H o -- • 



.co- 



in 






.2 S 



o o S 2 

2 2 °^ 

03:5 >> •- 

CO 



t; g > S 

S -H "^ ^ 

> 03 lO* ** "^ 

^ i "1= 

(V, '^ O) M > 

3 ?! A 



c3 ^ 

a ^ 

o3 oi 

a 



o C 



j3 » 03 '^ 
-I o 



03 



o o 

O 



tc -^ 3 

s ? ^ - 

r! ''-' .g <0 



S'V, '^ 

„ Sbco t^T3 
d 03 „t3 






h3 






REPRODUCTION 43 

artificial impregnation. The artificial insemination of 
the domestic animals, particularly cows and mares, has 
been practiced in various parts of the world for many 
years. As early as the time of Spallanzani ^ (1784) arti- 
ficial insemination was successfully accomplished in 
dogs. It seems probable also that the Arabs have been 
familiar with the possibilities of this practice for centuries.^ 
The insemination of mares, cows and bitches as a remedy 
for sterility has been demonstrated by Huish.^ The Rus- 
sian investigator Iwanoff ^ was successful in inducing 
pregnancy in rabbits and guinea pigs by artificial jneans. 
Artificial insemination is employed for the purpose of 
overcoming certain forms of sterility in mammals, specifi- 
cally, constriction of the muscles surrounding the neck 
of the uterus. It is also successful in cases of acid secre- 
tions of the vagina which are unfavorable to the proper 
functioning of the sperm-cells after they have been de- 
posited in the generative organs of the female. Artificial 
insemination is also a practical method of extending the 
usefulness of a valuable male, as by this means one male 
may be used successfully for breeding a much larger 
number of females. 

44. Methods of artificial insemination. — The most 
common methods in use are insemination with a specially 
made syringe or the introduction of the semen in capsules. 
By one method the semen is collected from the vagina 
of the mare after the service of the stallion by introducing 
the syringe into the vagina until the mouth of the syringe 

1 Spallanzani, "Dissertations," vol. II, 1784. 

2 Gautier, "Le Fecondation Artificielle," Paris, 1889. 

3 Huish, "The Cause and Remedy of Sterility in Mares, 
Cows and Bitches," London, 4th edition, 1899. 

^ Iwanoff, "De la Fecondation Artificielle chez les Mammi- 
feres," Arch, des Sciences Biologiques, vol. XII, 1907. 



44 THE BREEDING OF ANIMALS 

is immediately over the cup-shaped depression just in 
front of the cervix. The semen is then drawn into the 
syringe and the instrument introduced into the vagina 
of the mare to be artificially bred and pushed carefully 
through the neck of the womb to insure the depositing 
of the semen inside the uterus. Care should be taken 
not to introduce the point of the syringe into the opening 
to the bladder which is only five or six inches from the 
external opening of the vagina. The transfer of the 
semen to the waiting mare should be made without un- 
necessary delay and all instruments should be kept at 
body temperature during the operation. All instruments 
should be thoroughly sterilized in hot water before using. 

Many interesting questions of biological and practical 
interest are raised by the practice of artificial insemina- 
tion. How long after the semen is collected will it con- 
tinue to be potent? What external conditions such as 
cold, heat, light and air affect the vitality of the germ? 
How long does the semen retain its vitality within the 
reproductive organs of the female? Partial answers 
to these questions have been given through the investi- 
gations of Lewis.^ 

45. Conditions influencing the vitality of the sperm- 
cells. — The vitality of semen collected and preserved 
at different temperatures under laboratory conditions 
showed great variations. High temperatures were gen- 
erally unfavorable. At the end of one hour the percentage 
of semen which was alive and active was : at 33° C, 40 
per cent ; at 30° C, 45 per cent ; at 26° C, 85 per cent, and 
at 18° C, 90 per cent. At the end of two-and-one-half 
hours all the sperm-cells maintained at the temperatures 
of 33° C. and 39° C. were dead, while 65 per cent of the 

1 Lewis, Oklahoma Experiment Station, Bulletins 93 and 96. 



REPRODUCTION 45 

cells were alive at the temperature of 18° C, and 45 per cent 
of the cells kept at a constant temperature of 26° were 
still active. The sperm-cells from boars of several breeds 
showed similar behavior and in every case the higher 
temperatures were unfavorable. Semen kept at a tem- 
perature of 31 to 32° C. and exposed to the diffused light 
of the laboratory resulted in the death of practically all 
the sperm-cells at the end of seven hours. A portion of 
the same semen protected from the light by wrapping 
in black paper showed 40 per cent of the germ-cells alive 
at the end of the same time. The spermatozoa exposed 
to direct sunlight for ninety minutes were all killed, while 
the portion protected from direct rays of the sun showed 
80 to 90 per cent alive at the end of the same time. 

46. Effect of too frequent breeding on the sperm-cells. 
— Lewis ^ found that the number of sperm-cells in the 
semen collected from the first service of a vigorous stal- 
lion was 428,000 to a cubic millimeter. The stallion 
was permitted one service daily for nine days. The 
number of sperm-cells diminished rapidly until there 
were only 74,300 sperm-cells to a cubic millimeter at 
the ninth service. The continuous and frequent service 
of the stallion also resulted in weakening the vitality of 
the sperm-cells. The semen from the first service kept 
at constant temperature of 13 to 21° C. showed twenty- 
five per cent of the sperm-cells alive after six-and-one-half 
hours. The sperm-cells in semen collected from the 
ninth service showed only five per cent of the cells alive 
after six hours. Simple exposure to the air seemed to 
have no deleterious effect on the vitality of the sperma- 
tozoa. 

The standard of judging of the vitality of the sperm- 

1 Loc. cit., p. 35. 



46 THE BREEDING OF ANIMALS 

cells in this investigation was microscopic evidence of 
normal motion and as pointed out by Lewis this method 
does not necessarily measure the' ability of the sperm 
successfully to fertilize the ovum. The addition of water 
to semen seems to lower the vitality of the sperm-cells. 
The presence of urine also has a retarding influence on 
the activity of the spermatozoa. Sperm-cells kept in 
contact with rubber lose their vitality more quickly than 
when preserved in a glass retainer. 

47. Vitality of spermatozoa within the female genera- 
tive organs. — How long do the sperm-cells retain their 
vitality after being deposited in the generative organs 
of the female ? The answer to this question is of practical 
importance, as it has an important bearing upon the 
particular time or stage during the heat at which the 
union of the male and female will be most likely to result 
in offspring. 

The period during which perfectly healthy sperm-cells 
retain their vitality and power of motion under labora- 
tory conditions is comparatively short. And while 
the conditions for a longer period of vitality are pre- 
sumably much more favorable inside the generative 
system of the female, yet investigations on mares and 
sows ^ seem to point to the fact that the life of the sperm- 
cells in the uterus of the female is comparatively brief. 
This is contrary to the opinion of many practical breed- 
ers. It is generally believed that the spermatozoa retain 
their vitality in the reproductive organs of the female 
for a number of days. It is stated by some veterinary 
authorities ^ that the spermatozoa will live in the vagina 
or womb of the mare from six to twelve days under the 

1 Lewis, Oklahoma Experiment Station, Bulletin 96. 

2 Breeder's Gazette, vol. 43, 1903, p. 683. 



REPRODUCTION 47 

most favorable conditions. A normal alkaline solution 
in the uterus is the most favorable medium for the long 
continued vitality of the sperm-cells. It is very often 
the case that the secretions in the reproductive organs 
of the mare are acid and such a chemical condition is very 
unfavorable to the continuance of the life of the sperm. 
It is true that the sperm-cells will live but a few hours 
in such an acid medium as is sometimes found in the 
uterus. A study of the literature on the longevity of 
the sperm-cells in the female reproductive organs is 
somewhat confusing. It is probable that very consider- 
able differences exist in the vitality of the spermatozoa 
from different individuals, but even this is scarcely suffi- 
cient to explain the wide discrepancies reported by vari- 
ous investigators. Various authors ^ have reported the 
presence of live and motile spermatozoa in the uterus of 
dogs eight days after coition. Marshall and Jolly ^ found 
live sperm-cells in the vasa deferentia of the rabbit ten 
days after the removal of the testes, but all were dead at 
thirteen days. The sperm-cells of bats are reported by 
Benecke and others to be deposited in the female organs 
in the autumn, there to remain dormant until the follow- 
ing spring. Ovulation is induced by the warm weather 
of early spring and the spermatozoa which have lain 
dormant throughout the hibernating period become active 
and insemination occurs. In the domestic hen, accord- 
ing to Lillie,^ '^ The period of life of the spermatozoa 
within the oviduct is considerable as proved by the fact 
that hens may continue to lay fertile eggs for a period of 

1 Hertwig, "Handbuch der Entwicklungslehre." 

2 Marshall and Jolly, " The (Estrus Cycle in the Dog." Phil. 
Transactions. B., vol. 198, 1905. 

3 Lillie, "The Development of the Chick," 1908, p. 35. 



48 THE BREEDING OF ANIMALS 

at least three weeks after isolation from the cock. After 
the end of the third week the vitality of the spermatozoa is 
apparently reduced, as eggs laid during the fourth and fifth 
weeks may exhibit at the most abnormal cleavage, which 
soon ceases. Eggs laid forty days after isolation are cer- 
tainly unfertilized and do not develop."^ That the sperma- 
tozoa may continue to fertilize eggs in the hen for at least 
twenty days after coition is noted also by Spallanzani. 

The researches of Lewis ^ including records of twenty- 
five sows showed that in three cases only were the sperm- 
cells alive and active after twenty hours existence in the 
female organs of generation. In two cases live sperma- 
tozoa were collected from the uterus at the end of forty 
hours. In most cases the sperm-cells taken from the 
female organs were all dead at the end of sixteen hours 
after the sow had been bred to a healthy normal boar. 
The rupture of the Graafian follicles was found to occur 
almost universally during the last part of the heat. *' In 
no case were the follicles found ruptured during the first 
twenty-four hours of heat and in most of the cases a 
period of thirty hours elapsed after the first signs of heat 
before many of the egg-cells escaped from the ovary." 
In no case were the Graafian follicles found ruptured in 
sows which were examined early in the heat. In one sow 
ovulation did not occur until forty-five hours and in 
another case seventy hours after the beginning of heat. 
From the fact that in swine the duration of the vitality 
of the sperm-cells in the generative organs is so short and 
that ovulation occurs during the last part of the heat, it 
is apparent that sows should be bred during the last 
part of the heat. To be more explicit, the sow should 

1 Spallanzani, "Dissertations," vol. II, 1784. 

2 Loc. cit., p. 7 et seq. 



REPRODUCTION 49 

be bred not less than thirty hours after the beginning 
of heat. In practice, the animal-breeder may safely 
assume that the normal active existence of the sperm- 
cells in the uterus of mammalian animals is short and 
that therefore to insure successful conception, the actual 
service of the male should occur very near to the time 
when the heat is at its height. 

48. Effect of intoxication of the male parent on his 
offspring. — The fertilized egg may be so influenced by 
various environmental factors that the embryos arising 
from such eggs are affected in a definite way. Similar 
effects from factors calculated to influence the sperm- 
cells are much more obscure. It is very difficult from 
the very nature of the factors involved to influence the 
sperm-cell in such a definite way that the influence will 
directly modify the offspring. Observations on this 
point have been numerous but few experiments under 
proper control have been made. In all experiments 
conducted for the purpose of influencing the male germ- 
cells, it is necessary to work through the animal body. 
Under these circumstances it is not always easy to deter- 
mine with certainty whether the modifications resulting 
from various treatments are the direct result of the treat- 
ment on the sperm-cell or the secondary effects from the 
changes in the parental body itself. Among humans 
it is generally recognized that indulgence in alcoholic 
drinks by the male results in various defects in the off- 
spring. In one observation Lippich studied ninety-seven 
children conceived during intoxication. Of this number 
all were defective except fourteen.^ Among seven births 

^Stockard, "Effect of Intoxicating the Male Parent," Amer- 
ican Naturalist, vol. 47, p. 641 ; also Journal of Heredity, vol. 
5, Feb. 1914. 

E 



50 THE BREEDING OF ANIMALS 

from conceptions during drunkenness, Sullivan reports 
six as having died of convulsions and the seventh was still- 
born. Chronic alcoholism has been found to change the 
structure of the testicular glands. The children of lead 
workers are known to be sometimes defective. 

Stockard ^ has made some very interesting experiments 
which clearly show that the sperm may be so affected 
that the resulting offspring will be defective. As a result 
of mating normal female guinea pigs with males which 
were in a state of intoxication from inhaling alcohol fumes, 
many of the offspring were defective. *' Out of G9 full 
term young, of which 54 were born alive, only 33 have 
survived and many of these are small and excitable 
animals, and although not treated themselves have since 
given rise to defective offspring in several cases where 
they have been mated with another." 

If these results are confirmed, we must conclude that 
it is possible to modify the offspring by special treatment 
of the paternal parent. Some evidence is submitted 
by this investigation to show that the bad effects are not 
limited to the immediate offspring but are transmitted 
to subsequent generations. 

49. Effect of lead poisoning on the male germ-cells 
as indicated by the offspring. — That the children of 
fathers who work in lead-manufacturing industries are 
often defective has been observed for a long time. Cole ^ 
and Bachhuber have reported results of feeding lead 
acetate to rabbits and fowls. The treatments were 
given to male parents alone and these were mated with 
normal females. Injury to the offspring from such treat- 

^ Loc. cit. 

2 Cole and Bachhuber, "Proceedings of the Society for 
Experimental Biology and Medicine," 1914, XII, pp. 24-29. 



REPRODUCTION 51 

ments was frequent. The offspring of male rabbits 
treated with lead acetate were smaller and had distinctly 
lower vitality than the offspring of normal parents under 
similar conditions. The results from lead-poisoning of 
male fowls indicated that their offspring is of distinctly 
lower vitality than of offspring from normally healthy 
fowls. 

The importance of these investigations to the practi- 
cal breeder lies not in the fact that alcohol and other 
poisons may modify the male germ-cell and subsequently 
the offspring, but that the sperm-cell is capable of such 
reactions to environmental conditions that the progeny 
are profoundly changed or their development entirely 
prevented. If the offspring may be so modified through 
the sperm-cell by alcohol and lead acetate, then it is in all 
probability susceptible to other influences. It is a well- 
known fact that many conditions in ordinary breeding 
practice do modify the birth rate and the characters of 
the offspring. Certain feeds are known to have a more 
or less definite relation to the breeding powers. Investi- 
gations under proper control planned to test the influence 
of special feeds on the sperm-cell are lacking. At vari- 
ous times breeders have reported that alfalfa, clover, sugar 
and other materials when fed to breeding females have 
resulted in difficult conception or in weak offspring. 
Whether these feeding stuffs have an injurious effect on 
the male germ-cell is not known and cannot easily be 
determined in ordinary farm practice. 



CHAPTER III 
THE BREEDING SEASON 

The arrival of puberty or the breeding age in the 
domestic animals does not mean that the breeding func- 
tion is exercised . continuously thereafter. In the case 
of all animals, domestic and wild, there exists a certain 
periodicity in the process of reproduction. The iphys- 
iological activities which result in the propagation of 
young recur with a certain rhythm, and under normal 
conditions there is a definite period between the 
birth of young and the reappearance of reproductive 
activities. 

This rhythm may be disturbed by certain external 
conditions, although in the higher animals it recurs with 
considerable regularity. The reproductive functions are 
one of the first to be affected by a marked change in the 
environment. Breeders have long recognized this fact. 
It has been observed that a stallion or bull imported 
from Europe to America often fails to breed well the 
first year. The same condition has been found to exist 
in the case of mares and cows. 

50. Changed conditions. — Darwin has described how 
changes in the ordinary habits of animals may profoundly 
influence their reproductive functions. Animals in cap- 
tivity rarely breed. Elephants, tigers, lions and many 
other species when confined fail to breed at all or breed 

52 



THE BREEDING SEASON 53 

with great irregularity. Failure to breed under these 
conditions is not the result of a diseased condition of the 
generative organs ; as Marshall has said, " It would seem 
probable that failure to breed among animals in a strange 
environment is due not, as has been suggested, to any 
toxic influence on the organs of generation, but to the 
same causes as those which restrict breeding in a state 
of nature to certain particular seasons, in that the sexual 
instinct can only be called into play in response to definite 
stimuli, the existence of which depends to a large extent 
upon appropriate seasonal and climatic changes." ^ 

Among the domestic animals, the generative functions 
are more active in the spring season. This is true of 
the horse, the cow and the pig. Sheep breed more readily 
in the autumn. 

How much the increased sexual activity of the domestic 
animals may be due to climate and how much to the 
change in the food supply, it is not easy to determine. 
Food itself as distinct from climate has a direct influence 
on the breeding powers of animals. The green succulent 
grass upon which the animals feed in the spring may be 
the efficient cause of increased sexual activity at that 
season. The ewes that exhibit an increased tendency to 
reproduction in the autumn may be stimulated in a similar 
manner by the general abundance of fresh feed which is 
characteristic of that season. It has long been the cus- 
tom among skillful shepherds to provide fresh, succulent 
feed in abundance to ewes at the time of turning in the 
rams. This practice is called " flushing." The shepherds 
claim that this practice causes the ewes to come in heat 
more promptly and with greater regularity. It is also 
claimed that a larger number of lambs will be produced 

^ Marshall, "The Physiology of Reproduction," p. 5. 



54 THE BREEDING OF ANIMALS 

at lambing time as a result of this practice. It is undoubt- 
edly true that the practice stimulates sexual activity 
and does cause the ewes to come in heat with greater 
regularity. It is probable that this result is due both 
to the character of the feed and its abundance. 

The breeding season may be influenced by heredity. 
Certain breeds of sheep will breed readily at all seasons. 
The Dorset Horned breed comes in heat and breeds at 
all seasons, while most of the mutton and merino sheep 
breed readily only in the fall. Other conditions which 
are known to influence the breeding season in domestic 
animals are the kind of food, condition of the animal, 
age and breed. 

Evvard ^ has shown that sows gaining in weight when 
bred produced larger litters than sows that were fed only 
a maintenance ration. 

51. Phases of the breeding season. — The breeding 
season is divided into more or less distinct phases and 
these have been described and named by Heape ^ and 
Marshall as the prooestrum, oestrum, metoestrum and 
dioestrum. 

52. Prooestrum. — The first part of the sexual season 
is occupied by the prooestrum. This period is character- 
ized by marked changes in the generative organs, the 
uterus becoming congested, while in the later stages 
there is often a flow of blood from the external opening 
of the vagina. The prooestrum is the period often re- 
ferred to by breeders as the time when an animal is '' com- 
ing in heat " or coming in season.^ 

1 Evvard, in "Report of American Breeders' Association," 
191. 

^ Heape, Quarterly Journal of Microscopical Science, vol. 44, 
p. 1. 

^ Marshall, "The Physiology of Reproduction," p. 36. 



THE BREEDING SEASON 55 

53. (Estrum. — The oestrum may be referred to as 
the heat proper and represents the time when the female 
will receive the male. It is during this period that the 
peculiar symptoms well known to practical breeders are 
exhibited. This phase is characterized by unusual 
activity on the part of the animal. Great restlessness, 
constant movement and often great mental excitement 
are observed in animals which are in heat. The genital 
organs become congested. The mammary glands in 
animals not suckling young increase in size. The external 
genitals, particularly the vulva, become swollen and red 
and mucous and bloody excretions flow from the genera- 
tive organs. In many animals, there are frequent at- 
tempts at urination. The female sometimes utters loud 
cries or grunts, as in the sow. Cows, ewes and sows 
lose appetite, and get " off feed," often losing in weight. 
In all meat-producing animals, when the females are 
fattened for the markets, this is an economic loss to the 
feeder. In some sections, the larger feeders have spayed 
the heifers intended for fattening and thus prevented 
this loss. If the animal is bred and conception occurs, 
these periods of excitement are prevented, but pregnant 
fat animals are less valuable on the market and are always 
discriminated against by the buyer. 

54. Metoestrum. — The oestrum is followed by a 
gradual subsidence of the symptoms which characterize 
this period, provided coition does not take place and 
pregnancy result. In the latter case, oestrum is followed 
by gestation. If the female is not bred to the male during 
oestrum, the sexual excitement of the period gradually 
passes away and the animal returns to a normal condition. 

55. Dioestrum. — The dioestrum represents the time 
of rest for the generative system between the periods of 



56 THE BREEDING OF ANIMALS 

sexual activity. This varies greatly in different animals. 
Again quoting Marshall, " In some animals, such as the 
dog, the metoestrous period is followed by a prolonged 
period of rest or anoestrum. In others, such as the rat 
or the rabbit, the metcestrum may be succeeded by only 
a short interval of quiescence. This short interval, 
which sometimes lasts for only a few days, is called the 
dioestrum. This in turn is followed by another prooes- 
trous period, and so the cycle is repeated until the sexual 
season is over. Such a cycle (consisting of a succession 
of the four periods, prooestrum, oestrum, metcestrum, and 
dioestrum) is known as the dicestrous cycle. The num- 
ber of dicestrous cycles in one sexual season depends 
upon the occurrence or nonoccurrence of successful 
coition during oestrus. Thus, if conception takes place 
during the first oestrous period of the season, there can 
be no repetition of the cycle, at any rate until after parturi- 
tion. The cycle may then be repeated. If conception 
does not occur at any oestrus during the sexual season, 
the final metoestrous period is succeeded by a prolonged 
anoestrous or non-breeding period. This is eventually fol- 
lowed by another prooestrum, marking the commencement 
of a new sexual season. The complete cycle of events 
is called the oestrous cycle." ^ 

56. Puberty. — The reproductive functions are not ac- 
tive in the young mammal during its very early existence. 
The nutritive system during the same period is char- 
acterized by unusual functional activity and a high degree 
of efficiency. The food consumed during the early exist- 
ence of the mammal produces larger gains in live weight 
than the same food at any later period of its life. 

The growth processes continue to function with great 

1 Marshall, "The Physiology of Reproduction," p. 37. 



THE BREEDING SEASON 57 

activity for a certain period and the reproductive organs 
gradually develop until at a certain age, or stage of devel- 
opment, the essential organs are matured and begin 
to develop perfect germ-cells. The stage of develop- 
ment when the ovaries of the female produce perfect 
eggs is called the period of puberty and represents the 
beginning of the breeding season. The arrival of puberty 
in the female is accompanied by the ripening of the first 
ovum or egg and the appearance of the oestrum or heat. 
The beginning of puberty in the female is marked by 
certain characteristic changes. The mammary glands 
increase in size, the general activities of the body are 
accelerated and the animal performs certain actions that 
are peculiar to the period of the oestrum or heat. The 
coming of puberty in the male is likewise associated with 
certain bodily changes which are well recognized by the 
practical breeder. In the stallion, the neck, and partic- 
ularly the crest develops, and the forequarters generally 
are relatively better developed than the hindquarters. 
The most significant changes however, are physiological. 
The entire system assumes a state of greater activity. 
Not only the generative system is concerned in this change 
but all organs and functions of the body become more 
active. In the bull, the external and visible changes 
are an enlarging and thickening of the horns, and thicken- 
ing and enlarging of the neck and crest. The increased 
activity of males is indicated by greater restlessness, 
irritability and the development of a pugnacious tendency. 
Bulls and stallions often become vicious and unmanage- 
able and engage in deadly struggles for supremacy. 
These contests are also common among the males of wild 
animals. Such battles have been observed as common 
among stags and wild stallions. 



58 THE BREEDING OF ANIMALS 

57. Conditions influencing puberty. — The age at 
which puberty begins in the various breeds of the domestic 
animals is dependent upon the kind of animal, the 
breed, the food and general care of the young before 
puberty. Puberty in the mare comes between the ages 
of twelve and eighteen months. Under normal condi- 
tions, the stallion reaches the same stage at twelve or 
fifteen months. The cow and bull of the modern breeds 
of cattle under favorable conditions will reach this period 
at four to six months of age, but under ordinary condi- 
tions, not until they have attained the age of eight to 
twelve months. The ewe and ram of the mutton breeds 
will often arrive at the period of puberty at the age of 
five or six months, but generally will require longer. 
The sow and boar will reach puberty sometimes as early 
as three months of age, but generally at five to six months. 
The domestic hen has been known to lay eggs at the 
age of four-and-one-half months. 

The beginning of puberty is greatly influenced by the 
nutrition of the young animal. This influence begins 
with the foetus in utero. If the pregnant mother receives 
a generous supply of nutritious food during the period 
of gestation, the young will be better developed at birth. 
The reproductive system along with the other organs will 
have developed somewhat nearer to the stage of sexual 
completeness. If such generous nutrition is continued 
after birth, the young animal will reach the period of pu- 
berty at an earlier period than when fed on a poorer ration. 
At the Missouri Experiment Station, Eckles ^ has shown 
in an investigation comparing generous feeding with a 
lighter ration that the well-fed heifer on the average comes 
in heat 92 days earlier than those fed less generously. 

1 Eckles, "Dairy Cattle and Milk Production," p. 209. 



THE BREEDING SEASON 59 

68. The oestrum and lactation. — In many of the 
domestic mammals, the period of heat is influenced by 
lactation. Nursing the young may prevent entirely or 
retard the appearance of heat after parturition. Ewes 
seldom come in heat while suckling young. In the case 
of cows, the oestrum is retarded. There is much varia- 
tion in the length of the time elapsing between the birth 
of the young and the first appearance of heat in the cow. 
It is probably about sixty days, although it may recur 
earlier or later than this period. The sow will generally 
come in heat three days after giving birth to a litter of 
pigs, but the oestrus period does not again occur until 
after the pigs are weaned. A prominent breeder of Duroc 
Jersey hogs, S. Y. Thornton, says, " In many cases, a 
sow that is in good condition will come in heat the third 
day after farrowing. I have bred them at that time but 
seldom knew one to get with pig if she was suckling, but 
one that has lost her pigs will invariably get with pig 
from the first period which is usually the third day after 
farrowing. A sow will often come in heat when her 
pigs are four to six weeks old if she has been well fed." 
The distinguished breeder of Berkshires, A. J. Lovejoy, 
says, " Sows often show signs of heat on the third day 
after farrowing, and again at eight weeks after farrowing, 
while suckling. We find that after weaning a litter, 
a sow will usually ' come in ' in three to five days." 

The heat period in the mare is very irregular. The 
" foal heat " occurs in seven to nine days after foaling. 
The oestrum recurs in most mares throughout the nursing 
period. But some mares do not come in heat during the 
time they are suckling foals. It is a well-known fact 
that there is a strong tendency in some mares to breed 
only once in two years. In some of the smaller mammals, 



60 THE BREEDING OF ANIMALS 

pregnancy is common while the mothers are still suckling. 
This is true of the domestic rabbit, guinea pig and rat.^ 
' 59. Heat during pregnancy. — Animals do not nor- 
mally come in heat during pregnancy. The fertilization 
of the egg of the female by the sperm-cell of the male 
sets in motion a series of physiological phenomena which 
react upon the ovaries in such a way as to cause a cessa- 
tion of the heat periods. The ripening of eggs also does 
not normally occur during pregnancy. There are excep- 
tions to this rule among certain mammals which seem to 
be otherwise entirely normal. 

60. Super foetation. — It sometimes happens that a 
pregnant mammal will not only come in heat and exhibit 
the various phases of the oestrum, but will ripen an egg 
and if bred to the male will conceive. Such an occurrence 
is given the name of superfoetation. This condition is 
somewhat rare, but has been observed more frequently 
among mares than other domestic animals. The reason 
for this is probably due to the fact that the records of 
breeding are more carefully kept for mares than for cows, 
sows or ewes. It is difficult even among mares to deter- 
mine, when twins are born, whether these are the result 
of one mating or whether they may actually be of different 
ages. Such authentic cases as are known have been 
those observed in the mule-breeding districts of the United 
States. If the mare is first bred to a stallion and three 
or six weeks later to a jack, and twins are born, one a 
mule and the other a horse, there can be no doubt that 
these colts are of different ages. Such a result could 
only happen in mares which come in heat and ripen an 
egg during pregnancy. 

^ Heape, Quarterly Journal of Microscopic Science, vol. 44, 
p. 43. 



THE BREEDING SEASON 



61 



61. Examples of superf oetation. — The literature of 
animal-breeding is singularly lacking in records of au- 
thentic cases of superf oetation. The writer has through 
many years collected evidence of such cases in the mule- 
breeding districts of Missouri, and a few of these are 
recorded here : 

'' W. E. Carmichael of Shelby ville, Missouri, bred a 
mare to a stallion and thirty days later to a jack. At 




Fig. 11. — Normal and usual anterior presentation in mare. 

the end of the normal period of gestation the mare gave 
birth to twins, one a mule and the other a horse colt. 
They were both dead at birth." ^ 

A nine-year-old mare belonging to Eugene Rhodes of 
Fairfax, Missouri, was bred to a stallion in May. In' 
August she showed unmistakable signs of heat and was 
mated with a jack. In the month of January following 
she gave birth to a perfectly formed mule colt and a 



1 Mumford, "Amer. Cyclopedia of Agriculture,' 
p. 31. 



vol. Ill, 



62 THE BREEDING OF ANIMALS 

horse colt, the latter being considerably shriveled in 
appearance. 

A case is reported by F. K. McGinnis of a Texas bred 
mare belonging to Mr. Carmack. This mare was bred 
several times to a stallion during a period of six weeks. 
She continued to come in heat and the owner, conclud- 
ing that she was sterile with the stallion, bred her to 
a jack. She was mated with the jack a number of 
times during a period of two weeks. Her owner, finally 
despairing of ever getting the animal in foal, turned her 
out. At the end of eleven months from the time the 
mare was first bred to the stallion she dropped twin 
colts, one a horse and the other a mule. Both were 
dead at birth. 

An interesting example of superfoetation is recorded 
by J. F. White of Whitesville, Missouri, who bred a four- 
year-old mare to a saddle stallion on April 25, 1909. 
She came in heat again and was bred to a jack May 29, 
1909. She was again in heat June 12, 1909, and was bred 
at this period to the saddle stallion first mentioned. On 
May 11, 1910, the mare gave birth to perfectly formed 
twin colts. One of these was a mule and the other a 
horse colt. The mule died from illness at the age of three 
weeks. The mule colt was a male. The horse colt was 
a mare and developed into a perfect colt. These were 
the mare's first colts. 

A draft mare belonging to J. C. Spies of Newark, 
• Missouri, was bred to a jack. Later she was turned in a 
lot with her own two-year-old stud colt. The following 
spring she foaled a mule and a horse colt. The mule 
died at five days old. The horse colt lived and made a 
good horse. 

Cases of superfoetation where the same animal is the 



THE BREEDING SEASON 63 

sire of both twins are probably much more common than 
is generally believed. In such cases it is difficult to deter- 
mine whether the twins foaled at the same time are the 
result of the fertilization of two eggs ripened at one and 
the same heat period, or whether the eggs have been ripened 
at different periods some distance apart. 

A case of this kind has been reported by J. A. Finley 
of Troy, Missouri. In this case the mare was bred to a 
jack, and twenty-one days later she was found in heat 
again and was again bred to the same jack. At the end 
of a few months she aborted, losing twin mule colts. 
One of these was much better developed than the other. 
It seemed clear that the two colts were from different 
periods of heat, — in this instance, twenty-one days 
apart.^ 

The following examples are probably to be regarded 
as cases of superfoetation : — A sow belonging to O. 
Young of Hopkins, Missouri, gave birth to three pigs. 
The mother nursed them for four or five days, when she 
weaned them. Three weeks later the sow gave birth to 
eight pigs, six of which lived and became thrifty young 
hogs. 

A young ewe owned by A. Cassity of Linneus, Missouri, 
gave birth to twin lambs on February 13th. About 
six weeks later on March 30th, she gave birth to a third 
lamb. See Plate I. 

62. Recurrence and duration of the oestrum. — The 
occurrence and duration of heat are influenced by age, 
species, food supply, season, heredity and other conditions. 
The heat period persists in the domestic animals for one 
to fifteen days.^ The duration of the heat period is 

1 From letter to Geo. F. Nardin, dated June 24, 1912. 

2 Hill, "Bovine Medicine and Surgery." 



64 THE BREEDING OF ANIMALS 

shortest in the cow and sheep, being in these species 
usually from twelve to twenty-four hours.^ Mares come 
in heat seven or nine days after foaling. Bred at this 
time the mare is more certain to conceive. Dimon,^ 
an experienced horseman, says that there is no regular 
period for the return of heat in mares. If mares are well 
fed they may come in heat at any season, but are more 
generally in heat in the spring and fall.^ If the mare 
fails to become pregnant when bred on the ninth day 
after foaling, she will usually be in heat twenty-one days 
thereafter. Heat persists for five days and recurs every 
twenty-one days.^ Heat recurs in the cow three or four 
weeks after parturition and recurs every twenty-one days. 
The heat period recurs in sheep from seventeen to twenty- 
five days. 

In the sow the heat period will be observed three 
days after delivery and usually not again until the 
pigs are weaned. Heat again recurs three or four days 
after weaning the pigs and every twenty-one days there- 
after. 

63. Effect of ration on recurrence of oestrum. — The 
recurrence of the oestrum after delivery of the young is 
often influenced by the character of the ration. At the 
Wisconsin ^ Experiment Station, Hart, McCollum, Steen- 
bock and Humphrey found that pregnant cows fed on an 
exclusive corn ration came in heat in four to six weeks 
after the first calf. When the cows were fed a ration 

1 Weber, " Untersuchung iiber die Brunst des Rindes," Arch, 
f. Wissensch. u. Prakt. Tierheilk., 37 Bd., 1911. 

2 Dimon, "American Horses and Horse Breeding." 

3 Reynolds, "The Breeding and Management of Draught 
Horses." 

^Curtis, "Cattle, Horses, Sheep and Swine." 
^ Wisconsin Exp. Station, Bui. No. 17. 



THE BREEDING SEASON 65 

made up exclusively of wheat and its products, the first 
appearance of heat was from ten to eighteen weeks after 
calving. Fresh pasture also will often cause animals to 
come in heat earlier after delivery, and the oestrum will 
recur with greater regularity. 



CHAPTER IV 

GESTATION AND LACTATION 

From the time the egg is fertihzed until the young 
animal is able to live an independent life covers a period 
which is of the greatest importance to the growth and 
development of the individual and the mother. During 
this time all the physiological activities which are con- 
cerned with growth are at maximum efficiency; at no 
other period in the life of the animal is growth so rapid. 
Not only is the rate of growth very rapid, but the food is 
utilized much more economically. The stage of develop- 
ment which takes place in the uterus of the mother is 
the period of gestation. The period of lactation is the 
time during which the mammalian animal elaborates 
milk. 

GESTATION 

64. Indications of pregnancy. — If the animal comes 
normally in heat and is bred to the male during the heat 
period, conception occurs in the natural course of events 
and pregnancy begins as a result of successful conception. 
Significant physiological changes occur which are recog- 
nized by the breeder as evidences of pregnancy. Preg- 
nant animals do not normally come in heat. The chief 
evidence, therefore, that an animal is ''in foal," "in calf," 
" in pig," or " in lamb " is the cessation of the periodic 
appearance of the symptoms accompanying the period of 
the oestrum. If after breeding the mare does not come in 

66 



GESTATION AND LACTATION 67 

heat for thirty daj^s, she is probably safe in foal. The heat 
period in the mare persists for several days, and therefore a 
reappearance of evidences of heat shortly after breeding 
should not be regarded as significant. It is pointed out 
elsewhere that mares may sometimes come in heat and 
conceive again (see superfoetation), even though already 
pregnant. It is also true that some mares will persistently 
refuse the horse, even though not pregnant. In the cow 
a period of sexual quiescence for three weeks following her 
breeding with the bull is good evidence that she is safely 
" settled " and in due time will give birth to offspring. 

The beginning of pregnancy in an animal is often 
accompanied by a marked change of temperament. A 
nervous, excitable mare may become more gentle and 
docile. It is also true that some mares which when 
not pregnant are quiet and gentle with other horses 
become cross during pregnancy and evince a desire to 
fight other horses. This tendency increases as preg- 
nancy advances. Following conception the pregnant 
animal shows a tendency to lay on fat much more rapidly. 
Feeders sometimes take advantage of this tendency to 
finish heifers and sows rapidly for the market, but such 
a practice is to be condemned, as the meat from pregnant 
animals is less desirable for human food. As pregnancy 
advances, the abdomen becomes larger at the sides and 
below and the flank falls in. The loins become depressed, 
owing to the sinking of the spine due to the increased 
weight of the abdomen. This depression of the loins 
gives the croup bones the appearance of rising. The 
udder of the pregnant animal is not materially changed 
during the initial stages of gestation, but during the later 
stages this organ gradually expands and the teats become 
larger. A short time before parturition the udder be- 



68 ' THE BREEDING OF ANIMALS 

comes greatly swollen and a waxy substance exudes from 
the ends of the teats. In the cow the developing foetus 
may be observed externally after the fifth month of preg- 
nancy. If the cow is permitted to take a drink of very 
cold water, the movements of the young calf may be felt 
by pressing the hand against the flank just in front of 
the stifle. In the mare the same movements of the un- 
born foal may be observed from the seventh to the eighth 
month in a similar manner by pressing the hand firmly 
against the flank in front of the left stifle. 

65. Physical examination for pregnancy. — The exist- 
ence of pregnancy may be determined with considerable 
accuracy by examination through the rectum. The 
method of making this examination is described in such 
an admirable manner by Law ^ that it is quoted entire : 
'' Examination of the uterus with the oiled hand intro- 
duced into the rectum is still more satisfactory, and if 
cautiously conducted no more dangerous. The rectum 
must be first emptied and then the hand carried forward 
until it reaches the front edge of the pelvic bones below, 
and pressed downward to ascertain the size and outline 
of the womb. In the unimpregnated state the vagina 
and womb can be felt as a single rounded tube, dividing 
in front to two smaller tubes (the horns of the womb). 
In the pregnant mare not only the body of the womb is 
enlarged, but still more so one of the horns (right or left), 
and on compression the latter is found to contain a hard, 
nodular body, floating in a liquid, which in the latter 
half of gestation may be stimulated by gentle pressure 
to manifest spontaneous movements. By this method the 
presence of the foetus may be determined as early as the 

1 Law, "Diseases of the Horse," U. S. Department of Agri- 
culture, p. 155. 



GESTATION AND LACTATION 69 

third month. If the complete natural outHne of the virgin 
womb cannot be made out, careful examination should 
always be made on the right and left side for the enlarged 
horn and its living contents. Should there still be diffi- 
culty, the mare should be placed on an inclined plane, 
with her hind parts lowest, and two assistants, standing on 
opposite sides of the body, should raise the lower part of 
the abdomen by a sheet passed beneath it. Finally the ear 
or stethoscope applied on the wall of the abdomen in front 
of the stifle may detect the beating of the foetal heart (one 
hundred and twenty-five per minute) and a blowing sound 
(the uterine sough), much less rapid and corresponding to 
the number of the pulse of the dam. It is heard most 
satisfactorily after the sixth or eighth month and in the 
absence of active rumbling of the bowels of the dam." 

66. The period of gestation. — The period of develop- 
ment from the fertilization of the egg by the sperm-cell 
until the birth of the fully developed offspring capable 
of independent existence outside the body of the mother 
is known as the period of gestation. Among oviparous 
animals it is the period of incubation. This period varies 
greatly as between different species, but under normal 
conditions is fairly uniform in animals belonging to the 
same species. The normal period of gestation has in 
general a more or less definite relation to the size of the 
animal. The length of gestation in animals as reported 
by various authors ^ is as follows : 

iNathusius, "Zool. Garten Jahrg.," 3, 1862. 

Heape, "The Sexual Season," Quarterly Journal of Micro- 
scopical Science, vol. 44, 1900. 

Ewart, "The Development of the Horse," Quarterly Journal 
of Microscopical Science. 

Wortley Axe, "The Mare and the Foal," Journal of the Royal 
Agricultural Society, 3d series, vol. IX, 1898. 



70 THE BREEDING OF ANIMALS 

Elephant 20 to 23 months 

Giraffe 14 months 

Dromedary 12 months 

Buffalo 10 to 12 months 

Camel 13 months 

Jennet 12 months 

Seal 11 to 12 months 

Mare 11 to 12 months 

Zebra and Celtic Pony .... 334 to 338 days 

Prjewalsky's Horse 356 to 359 days 

Cow 9 months 

Bear 6 months 

Reindeer 8 months 

Monkeys 7 months 

. Sheep and Goat 21 to 22 weeks 

Sow 4 months 

Lion 3^ months 

Dog 59 to 63 days 

Fox and Wolf 63 to 63 days 

Guinea Pig 61 days 

Cat 63 days 

Polecat 40 days 

Rabbit 30 days 

Squirrel and Rat 28 days 

Mice 21 days 

Small breeds require a shorter time than larger breeds, 
but this influence may be overcome in breeds which have 
long been selected for early maturity. According to 
Youatt/ all domestic animals are subject to considerable 
variation in the length of gestation both above and below 
the normal period. Tessier ^ has observed a large num- 
ber of pregnant females among the domestic animals 
and has reported marked variations in the time required 
for complete development of the foetus and final expul- 
sion from the uterus. This authority has reported on 
582 mares in which the period of gestation ranged from 

1 Youatt, "Cattle," p. 521. 

2 Tessier, "Recherches sur la Duree de la Gestation," Mem. 
de I'Acad. des Science, Paris, 1817. 



GESTATION AND LACTATION 



71 



287 to 419 days. Among 1131 cows the length of the 
period varied from 240 to 321 days. The minimum gesta- 
tion period among 912 sheep was 146 days and the maxi- 
mum 161 days. It is of interest to note, however, that 
among 676 ewes the period varied from 150 to 154 days 
only. 

The Earl of Spencer ^ found the period to vary from 
220 to 313 days in cows. The following table includes 
the observations of a number of investigators and is useful 
as indicating the somewhat wide variations which may 
occur in the gestation period of the domestic animals : 

Period of Gestation in Domestic Animals ^ 



Mares 

Mares 

Cows 

Cows 

Cows 

Cows 

Cows 

Ewes 

Ewes 

Sows 

Sows 



numbek of 
Cases 



582 

25 

575 

764 

50 

98 

182 

912 

420 

25 

10 



Maximum 
Days 



419 
367 
299 
285 
291 
299 
296 
161 
156 
123 
116 



Minimum 
Days 



287 
324 
240 
220 
268 
276 
280 
146 
143 
109 
101 



Authority 



Tessier 

Gayot 

Tessier 

Spencer 

Allen 

Bement 

Wing 

Tessier 

Magne 

Tessier 

Fox 



1 Journal of the Royal Agricultural Society, vol. I, pp. 166, 167. 

2 See Tessier, Journal of the Royal Agricultural Society, vol. I, 
pp. 166, 167. 

Franc k-Albrecht-Goring, " Die Trachtigkeitsdauer," Thier- 
artzliche Geburtshiilfe, vol. 4, 1901. 

Wing, Cornell Experiment Station, Bui. 162. 
Smith, "Physiology of the Domestic Animals." 
Allen, "American Cattle," p. 259. 
Miles, "Stock Breeding," 1907, p. 400 et seq. 



72 THE BREEDING OF ANIMALS 

The period of gestation in the domestic jennet is 
370 days. Careful records kept by Kalo Monsees ^ 
on the large jack- and jennett-breeding farm of Monsees 
and Sons at Smithton, Missouri, indicates that the maxi- 
mum gestation period for a living colt was 13 months 
and 16 days. The minimum period was 11 months and 
15 days. The average period was 370 days. These 
figures may be taken as reliable since they cover a large 
number of animals of varying ages and sizes for several 
years and represent the progeny of different jacks. 

67. Causes of variation in length of gestation period. — 
The causes of variations in the time required for the 
development of the young in the uterus are not always 
clearly apparent. It is probable that prolonged gesta- 
tion may sometimes be due to the mother suckling young 
during pregnancy, resulting in providing an insufficient 
supply of food to the developing foetus.^ Tessier con- 
cludes that the length of the period of gestation does 
not depend upon age, constitution of the female, diet, 
breed or season. Nathusius ^ and others have found 
that comparing races and breeds belonging to the same 
species, those which have been selected for their early 
maturing qualities have a shorter gestation period. 
Darwin '* has given some evidence of this in connection 
with the grading up of Merino sheep bred to the earlier 
maturing Southdown. The length of gestation is given 
as follows : 

^ Kalo Monsees, "Breeding Records of Monsees and Sons Jack 
and Jennett Breeding Farm." 

2 Pinard, "Gestation," Richets Dictionnaire de Physiologie, 
vol. 7, Paris, 1905. 

' Loc. cit. 

^ Dar^vin, "Animals and Plants under Domestication," vol. 
1, p. 123. 



GESTATION AND LACTATION 73 



Merinos 

Southdowns 

Half blood Merino and Southdown 
Three quarter blood Southdown . 
Seven eighths blood Southdown . 



150.3 days 

144.2 days 

146.3 days 
145.5 days 
144.2 days 



Some doubt has been expressed as to the authenticity 
of the maximum period of gestation in mares. The edi- 
tor of the Breeder's Gazette commenting on this fact says, 
"Mares are usually credited with pregnancy lasting eleven 
months. When they run twelve months we prefer to 
believe that the date has not been properly kept. We 
believe that forty-eight weeks, seven days to the week, or 
326 days is about the average duration of pregnancy in 
a mare.'' ^ Referring to this statement M. W. Johnson ^ 
of Illinois writes that he has been in the breeding business 
for fourteen years and has complete records on the breed- 
ing of 5000 mares. He reports one mare as having carried 
her foal for twelve months and sixteen days and another 
for twelve months and eighteen days. Both foals were 
deformed. Another mare gave birth to a perfectly 
healthy foal at the end of one year and eighteen days while 
another carried her foal exactly thirteen months and 
dropped a healthy foal. A Percheron mare belonging to 
H. F. Sperry ^ dropped a mule colt twelve months and 
two days after breeding. William Lokings of South 
Dakota owned a pony mare which was twice bred and 
gave birth to a foal twelve months and twenty-five days 
after the last service. There is a popular belief that 
male offspring are carried longer than female. Bement ^ 
found that the average length of gestation for male calves 

1 Breeder's Gazette, May 15, 1907. 

2 lUd., June 19, 1907. 

3 Ibid., June 26, 1907. 

4 The Cultivator, 1845, p. 207. 



74 THE BREEDING OF ANIMALS 

was 288 days and for females 283 days, but in 1839 the 
female calves were carried longer than the males. Earl 
Spencer ^ also believed there was some relation between 
sex and the length of gestation. M. Magne ^ found the 
period of gestation longer for ewe lambs than for ram 
lambs. C. U. Connellee ^ of Texas finds no relation be- 
tween the sex of foals and the time required for gestation. 
The evidence available is insufficient to justify the belief 
that male offspring are carried longer than females. 

68. Incubation. — The period of incubation in fowls 
represents in oviparous animals the phenomenon of gesta- 
tion in mammals. The length of the period of incubation 
among domestic birds is given by Miles ^ as follows : 

'' Turkey, twenty-six to thirty days ; guinea hen, 
twenty-five to twenty-six days; pea-hen, twenty-eight 
to thirty days; ducks, twenty-five to thirty-two days; 
geese, twenty-seven to thirty-three days ; hens, nineteen 
to twenty-four days, or an average of twenty-one ; pigeons, 
sixteen to twenty days; canary-birds, thirteen to four- 
teen days. Mr. Wright remarks that ' cold weather, or 
a prevailing east wind, will lengthen the time a day or 
more, while warm weather and an attentive sitter will 
hasten it ; stale eggs also hatch later than fresh.' " 

The smaller breeds, like bantams, hatch in nineteen 
or twenty days, while the heavier breeds may require 
as long as twenty-two days for complete incubation. 
When eggs are artificially incubated, it has been found 
that a higher temperature combined with favorable 
moisture conditions will shorten the period. 

1 Spencer, Journal of the Royal Agricultural Society, vol. 1, 
p. 168. 2 Loc. cit. 

3 Breeder's Gazette, June 26, 1907. 

4 Miles, "Stock Breeding," p. 401. 



GESTATION AND LACTATION 75 

69. Parturition. — In mammalian animals at the end 
of the period of gestation and in the normal course of 
events, the fully developed foetus is expelled from the 
uterus. This phenomenon is known as parturition. The 
beginnings of parturition are accompanied by a series 
of rhythmic contractions (labor pains) of the uterus which 
eventually result in the birth of the offspring. These 
contractions are at first partially controlled by the will, 
but later are entirely involuntary. That the muscular 
movements of the uterus are not controlled entirely by 
the central nervous system is shown by the researches 
of Kehrer,^ Helme and others. These investigators found 
that a healthy uterus may rhythmically contract when 
separated from the body if it is maintained at body tem- 
perature without important variations. The powerful 
muscular contractions of the uterus of mammals are 
characterized by the mechanical stretching of the bag of 
membranes by severe contraction of the longitudinal 
muscle fibers and the relaxation of the circular fibers of 
the cervix. The contraction of the uterus and the relaxa- 
tion of the cervix causes the bag of membranes to act as 
a fluid wedge still further extending the neck of the 
womb. These phenomena are followed by the head and 
fore legs of the young animal, the rhythmic contractions 
become more frequent and more powerfully exerted, and 
these are supplemented by the abdominal muscles in 
the final stages of parturition. The immediate inciting 
causes of parturition are not well known. Various 
explanations have been attempted. Spiegelberg ^ has 
suggested that the foetus secretes a substance which 

1 Marshall, " The Physiology of Reproduction," p. 527. 

2 Spiegelberg, "Die Dauer der Geburt," Lehrbuch der Geburts- 
hiilfe, vol. II, 1891. 



76 THE BREEDING OF ANIMALS 

finally entering the maternal blood reaches the nerve 
centers and through them acts on the uterine nerves 
in the spinal cord. Beard ^ and others have held 
that there is an intimate relation between the oestrus 
cycle and parturition. It is known that abortion is 
more apt to occur at the time of the periodical return of 
heat. But may it not be true that the period of gesta- 
tion is itself governed by a certain rhythmic law or peri- 
odicity similar to that which brings about the heat period ? 
Other possible explanations are that the placenta begins 
to decay or atrophy at the end of a given period and thus 
loses its hold on the uterine walls, and the waste products 
thus developed may furnish the real stimulus which 
results in parturition.^ The death of the foetus prema- 
turely will generally bring on expulsive movements of 
the uterus and speedily relieve the uterus of its dead 
burden. 

It is probable that the causes of parturition are very 
complex and that a combination of the above, together 
with other causes, may bring about eventually the suc- 
cessful birth of the young mammal after the normal 
period of existence in the uterus.^ 

70. Normal parturition of the domestic animals. — 
Under ordinary conditions and in due course of time, the 
young of the domestic animals are born without diffi- 
culty. When difficult parturition occurs, it may be due 
to mal-presentation of the foetus, malformation of the 
foetus, malformation of the mother, or disease of the mother 
preventing the normal expulsion of the foetus. 

1 Beard, "The Span of Gestation and the Cause of Birth," 
Jena, 1887. 

-WilUams, "Obstetrics," London, 1904. 
^ See also Marshall, loc. cit. 



GESTATION AND LACTATION 



77 



71. Mal-presentations. — In order that the offspring 
may be successfully expelled from the generative organs 
of the mother, it is necessary that it should approach 
the neck of the uterus in a certain form or '' presentation." 
In all the mammalian domestic animals the normal pres- 
entation is one in which the fore legs are extended for- 
ward with the nose also extended forward and lying 
between the knees. (See Fig. 11.) In case of twins, 




Fig. 12. — Parturition in mare. Posterior presentation. 

the second is generally presented with the hind feet first. 
(See Fig. 12.) Any other presentation than the two here 
described is abnormal, and the birth of young under such 
conditions is difficult or impossible. 

As most cases of difficult parturition are due to abnormal 
presentations, it is important that the more common 
mal-presentations should be mentioned. The more com- 
mon and difficult mal-presentations are : — head normal, 
but fore legs bent back at the knee (Fig. 13) ; head normal, 
but fore legs bent back from the shoulders and entirely 



78 



THE BREEDING OF ANIMALS 




Fig. 13. — Abnormal anterior presen- 
tation. 



under the body ; fore feet normal, but head bent to one 
side or downward ; fore legs normal, but the head bent 
backward and upward; all four feet presented; thigh 
and croup presented first, with hind legs bent under 

body (Fig. 14) ; the back 
first presented, with fore 
and hind legs extending 
backward toward the 
uterus (Fig. 15). 

72. Normal presen- 
tations. — In the early 
stages of parturition, 
it is desirable to deter- 
mine whether the foetus 
is normally in position 
to be expelled with least 
difficulty. As already described, the normal presenta- 
tion is head and fore legs forward, or in some cases 
(twins) the hind legs forward. In making the examina- 
tion for the purpose of determining whether the foetus is 
in proper position, the hand and arm should be thoroughly 
cleansed and oiled 
with vaseline, and 
inserted into the 
vagina and an ex- 
amination made. 
The manipulation 
should be conducted 
with extreme gentle- 
ness and under such conditions as shall not excite the 
pregnant animal. Advantage should be taken of the 
lulls in the labor pains to make the examinations. While 
the muscular contractions are on in full force, little can 




Fig. 14. — Abnormal posterior presentation. 



GESTATION AND LACTATION 79 

be accomplished. If the foetus" is found to be normally 
presented, it is always wise to let nature take her course, 
and in most cases birth ensues without assistance from 
the attendant. 

73. Treatment for mal-presentation. — If the exam- 
ination reveals the fact that the foetus is not normally 
presented, an effort should be made to readjust the 




Fig. 15. — Abnormal transverse presentation. 

unborn animal so that it will be normally presented. 
In the case of valuable breeding animals, it is generally 
best to secure at once the services of a skilled veterinarian. 
In attempting to make the readjustment of the foetus, 
the same care and gentleness should be exercised as in 
the initial examination. In order that the mal-presenta- 
tion may be successfully adjusted and the fore legs and 
head properly brought forward into the cervix and vagina, 
it will be necessary to push the foetus back into the uterus 
where there will be sufficient room for the manipulation. 



80 THE BREEDING OF ANIMALS 

If the labor pains have already proceeded for some time, 
it may at first be found somewhat difficult to return the 
foetus to the uterus. In all cases it will be useless to 
attempt to push back the unborn animal during the severe 
labor pains. But as the resting period and consequent 
relaxation follow each severe contraction, the foetus may 
be gradually pushed back. It is sometimes helpful par- 
tially to suspend the hind quarters of the pregnant mother 
by roping the feet and hoisting the hind quarters so that 
they will be somewhat higher than the forequarters, and 
in this position it is generally easier to accomplish the 
return and readjustment. In most cases in which the 
foetus and mother are in normal health and condition, 
the foetus may be expelled without great difficulty after 
readjustment, that is, provided the mother has not 
become too severely exhausted by long-continued labor. 
In such case it is necessary to render aid by supplement- 
ing the mother in her efforts to expel the foetus.^ 

LACTATION 

The young of most mammalian animals are born into 
the world in an immature and often quite helpless condi- 
tion. In most species the newborn animal is unfit to 
live and thrive independently. In particular the nutri- 
tive functions of the very young mammal are not 
developed to a point where the individual can immedi- 
ately exist on the food consumed by the mature parent. 
To provide nourishment for the very young animal, all 
mammals are provided with mammary glands which 
secrete milk. 

^See Law, " Diseases of Cattle," 1908, and " Diseases of tlie 
Horse," 1907, U. S. Department of Agriculture. 



GESTATION AND LACTATION 81 

74. The mammary glands. — All mammals are supplied 
with milk-secreting glands. These glands are present 
in both sexes, but are rudimentary in the male. In the 
female the glands are large and are stimulated into active 
functioning by the exercise of the reproductive organs. 
In the immature female before the arrival of puberty, 
these glands are small and inconspicuous. With the 
first appearance of puberty accompanied by the oestrum, 
the glands increase in size. 

The number of glands present varies with the species. 
In some animals which normally give birth to one offspring 
at a time, as in man, there are two glands (mammae). 
In the cow, however, normally producing one at a birth, 
the normal number of mammae is four. In cats, dogs, 
rabbits and swine, species producing from four to twenty 
young at one time, there are normally present several 
pairs of mammae. Wentworth found the number of 
mammae in swine to vary from nine to fourteen.^ There 
is, therefore, a rather definite relation between the num- 
ber of mammae and the normal number of young pro- 
duced at each birth. This relation does not seem to be 
important as an index of fertility in any particular species. 

75. The duration of lactation. — Among wild forms the 
continuance of lactation varies widely in different species. 
In general the period of lactation ends when the young 
animal has developed to a point where it can live in- 
dependently and secure its nourishment in the same way as 
the^mature individual. In the case of the domestic cow, 
the milking function has been developed and stimulated 
under domestication to a point where the lactation period 
may persist from one calving period to the next without 

1 Wentworth, "Inheritance of Mammae in Dm-oc- Jersey 
Swine," American Naturalist, vol. 47, 1913. 

Q 



82 THE BREEDING OF ANIMALS 

intermission. The more important conditions which in- 
fluence the duration of lactation and the amount of milk 
produced among the domestic animals are food supply, 
habit, heredity, exercise, climate and nervous excitement. 

76. The food supply. — Every mature domestic animal 
requires a certain minimum amount of food to maintain 
the ordinary bodily functions. This is called the food 
of maintenance. The function of milk-giving must be 
regarded as an additional requirement. The animal, 
therefore, that is producing milk must consume and 
assimilate larger quantities of food than one that is dry 
or not producing milk. It follows that the greater the 
amount of milk produced, the larger the demands of the 
lactating animal for food. In an ordinary cow in full 
milk, the food of maintenance may represent sixty per 
cent of all the food eaten. In this case forty per cent 
of the ration is available for milk production. In a 
heavy-producing cow, the food of maintenance may 
represent only forty per cent of the whole. In the latter 
case, as much as sixty per cent of the ration may be utilized 
for milk production. The greater economy of production 
in the case of the heavy-producing cows is at once appar- 
ent. If an insufficient ration is fed to any cow in full 
milk, the first effect will be to cut down the milk flow. 

77. Habit. — The duration of the lactation period is 
materially influenced by the habit of the cow as deter- 
mined by man. The lactation period of a cow, which is 
normally ten months, may be shortened by careless milk- 
ing or insufficient feeding. The milking function may be 
so stimulated by careful and thorough milking and intelli- 
gent feeding that the daily quantity of milk may be 
increased and the period of lactation lengthened. 

78. Heredity. — The capacity to give milk in abundance 



GESTATION AND LACTATION 83 

is hereditary. The present highly productive dairy breeds 
owe their greater abihty to produce large quantities of milk 
to their inheritance of this quality from their ancestors. 
In the same breed certain families are known to possess the 
quality of large capacity for milk production to a higher de- 
gree than the average of the breed. It is also true that the 
duration of the period of lactation is influenced by heredity. 

79. Exercise. — An excessive amount of muscular 
exertion of any kind must be regarded as unfavorable 
to the maximum production of milk. Cows that are 
required to travel long distances over sparse pastures 
in order to secure sufficient food for their needs cannot 
produce their maximum quantity of milk. In many 
European countries, cows are generally employed as 
draft animals in the ordinary farm operations of plowing, 
harrowing, reaping and other work. Investigations in 
Germany have shown that so long as cows are employed 
at moderate work the milk flow is not decreased. When- 
ever cows were compelled to work at heavy labor and 
for long hours, invariably the flow of milk was decreased. 

80. Climate. — Exposure to extreme dry cold or to cold 
driving storms will have the effect of decreasing the normal 
milk yield of a herd of cows. In general, a lack of ade- 
quate shelter in a cold and humid climate may seriously in- 
terfere with the highest development of the milking func- 
tions. A herd of cows will produce more milk in winter 
if provided with water which has been slightly warmed. 

81. Unusual lactation. — In general, lactation is closely 
associated with reproduction. Pregnancy followed by 
parturition normally precedes the secretion of milk in 
the mammary glands. Males and sterile females possess 
rudimentary mammae but seldom secrete milk, although 
a number of cases are on record where males have been 



84 



THE BREEDING OF ANIMALS 



known to secrete milk. The hybrid mare mule in rare 
cases has been known to secrete milk through the excita- 
tion of the mammary glands. In the cases observed, 
the mammary glands have generally been stimulated 
to secrete through the persistent suckling of some young 
mule colt which may have been running in the same 
pasture or lot. It is rare that the mammary glands of a 
mare mule will develop to the point of secreting milk 
in the absence of some such stimulation. 

The author has discovered one mare mule which has 
secreted milk without any such stimulus. This mare 
mule belonging to L. O. Swarner of Boonville, Missouri, 
when first observed had been giving milk for some weeks. 
The owner in a letter to the author says : "I have a mule 
that has been giving milk the same as a brood mare does 
when suckling a colt. She has been giving milk for about 
five weeks. The mule is still giving milk, as much as a 
quart at a time. (See Plate III, upper.) The milk is pure 
white and streams from her udder." This mare mule 
came in heat regularly and was bred several times but 
failed to become pregnant. The milk was analyzed by 
the Missouri Experiment Station. The analysis is shown 
in the table in comparison with cow's and human milk : 



Composition op Milk from Mare Mule Compared with 
Cow's AND Human Milk 





Mare Mule 
"Beck " 


Cow's Milk 


Human Milk 


Water 


90.441 % 


87.17% 


87.41 % 


Total Solids 


9.559 


12.83 


12.59 


Ash 


0.400 


0.71 


.31 


Fat 


1.450 


3.64 


3.78 


Protein 


2.463 


3.55 


2.29 


Sugar 


5.792 


4.88 


6.21 





Plate III. — Upper. A mare mule that gives milk. Lower. A 
Free-Martin heifer that proved fertile. 



CHAPTER V 
FERTILITY 

The larger number of the breeders of domestic animals 
are engaged merely in the multipHcation of animals. 
They are not primarily striving for the improvement of 
the species. To all these, the ability of an animal to 
produce young in abundance is of fundamental impor- 
tance. To the relatively small class of breeders who are 
successful in really improving the desirable characteristics 
of existing breeds, the quality of fertility is likewise of 
primary importance. When the breeder has succeeded 
in developing a highly improved strain, it becomes im- 
portant to secure as many offspring possessing the new 
and desirable qualities as possible. 

Fertility may be defined as the ability of an animal 
to produce young in abundance. This quality depends 
upon the number of young born at one time, the fre- 
quency of the recurrence of the oestrum, the duration of 
the period of gestation, and the length of the period of 
life during which reproduction occurs. All of the above 
conditions are affected by many circumstances, some 
external, others internal and inherent in the individual 
and the species. Many of the circumstances influencing 
fertility can be directly or indirectly controlled by man, 
others are beyond his control. 

82. The number of young at a birth. — There is very 
great variation among animals in respect to the number 

85 



86 THE BREEDING OF ANIMALS 

of young born at one birth. This difference is very 
marked, as between different species, for example, as 
between the sow and the ewe. A similar difference is 
likewise to be observed between individuals and families 
belonging to the same species. In a general way, the 
number of young carried in the uterus at one time seems 
to depend upon the size of the animal. Thus the ele- 
phant, rhinoceros, hippopotamus, giraffe, bison, domes- 
tic mare and cow, produce one young at a birth. The 
goat and sheep, while normally producing one offspring 
at a time, may frequently produce twins and triplets or 
even a larger number at one birth. 

The hare and rabbit are much smaller than the sheep 
and are very much more prolific. The wild rabbit pro- 
duces from four to eight in a litter. The domestic rabbit 
is more prolific than the wild, often giving birth to eight 
or ten at one time. 

The lion and tiger in a wild state give birth to two to 
three cubs, while the domestic cat will sometimes produce 
as many as nine. The size of the litter in the fox is from 
four to eight. The number of young in the litter of the 
domestic dog varies from five to twelve. 

The domestic sow is an exception to the general rule 
that smaller species are more prolific. The sow is the 
most prolific of the more important domestic animals, 
though not the smallest. The wild sow's litter numbers 
four or five. The domestic sow produces from seven to 
twelve, and much larger litters are common. 

The smaller rodents, like the rat and mouse, are char- 
acterized by large litters. The rat regularly gives birth 
to twelve or fifteen young at a time and has been known 
to produce twenty at one birth. The mouse is equally 
prolific. 



FERTILITY 87 

It does not seem to be generally true among domestic 
animals that the smaller breeds are more fertile than the 
larger breeds of the same species. Among sheep, the 
American Merino and Southdown are relatively small 
breeds, but are less prolific than the larger Shropshire, 
Cotswold or Lincoln. The smaller breeds of swine, 
like the Essex, Cheshire and Small Yorkshire, are in 
general less prolific than the larger Berkshire, Duroc- 
Jersey and Large Yorkshire. In this instance, it is 
probable that selection by man has intervened to counter- 
act the general law that the smaller animals are more 
fecund. 

83. Period of gestation and fertility. — The length of 
the period of gestation seems to be some index of the 
number of young produced at a birth. In all animals 
requiring a longer period of gestation than six months, 
one is the normal number of young at a birth. ^ Among 
the animals in which the period is less than six months 
are the hog, sheep, goat, rabbit, dog, cat, rat and mouse. 
In all of these, except the sheep and goat, the normal 
number is greater than one. The sheep and goat under 
domestication have so increased in fertility, in the cases 
of some breeds at least, that fecundity is much greater 
than in the horse or cow, where single births are the rule. 
Milch goats usually drop twins, and triplets are not rare.^ 

The Border Leicester breed in England has produced 
150 to 160 per cent of lambs under ordinary conditions. 
When the same breed has been specially fed before breed- 
ing, the number of lambs has been increased to 200 per 
cent. 

1 Marshall, "The Physiology of Reproduction." 

2 Clos, vol. Ill, p. 410, "Cyclopedia of American Agri- 
culture." 



88 THE BREEDING OF ANIMALS 

84. Fertility and the frequency of the recurrence of the 
oestrum. — The fertility of animals is also dependent 
upon the frequency of the recurrence of the oestrum. 
As already described, the recurrence of heat depends 
upon a number of conditions, chief of which are 
pregnancy and lactation. Certain of the domestic 
animals do not normally come in heat while suckling 
young, but to this there are many exceptions. Animals 
having a short period of gestation rarely or never come 
in heat while suckling young. 

85. Fertility and gestation. — Animals having a long 
period of gestation are less fertile than animals requiring 
a shorter time for the development of the young in the 
uterus. 

The exceptional fertility of the domestic sow is due 
not only to the large number of young born at a time, 
but to the further fact that the period of gestation is 
only four months. A sow may thus easily produce 
two litters a year. The mare produces but one off- 
spring at a time, and the period of gestation is from 
eleven to twelve months. A sow, therefore, may give 
birth to twenty young in the same period of time re- 
quired by the mare for the development and birth of 
one offspring. 

86. Duration of the reproductive period. — The fertility 
of an individual or a breed is largely determined by the 
duration of the reproductive period. The length of 
this period is a matter of special importance in the larger 
animals which produce but one young at a birth. The 
breeding age is the time from the arrival of puberty 
until the cessation of the breeding function on account 
of old age. The beginning of the reproductive period 
has already been discussed under puberty. The 



FERTILITY 89 

average age at which the domestic animals cease to 
breed is difficult to determine because of the scarcity of 
records on this point. The persistence of the breeding 
powers of the domestic animal is influenced by the condi- 
tions under which they are reared. With favorable 
conditions, the mare has produced young regularly until 
twenty-five years old. Ewes have continued to produce 
offspring until nineteen years of age. 

87. Confinement and fertility. — The close confine- 
ment of animals seriously interferes with their fertility. 
Wild animals like the elephant, tiger, lion, squirrel and 
monkey in captivity are often sterile. Darwin states 
that the same animals breed more readily in traveling 
shows than in zoological gardens. Among the domestic 
animals, confinement and lack of exercise are frequent 
causes of a low degree of fertility. It is generally a mis- 
take to confine ewes or sows in a small lot during the 
winter months, under conditions which make it impossible 
for them to secure adequate exercise. The same may be 
said of males, including stallions, bulls, boars and rams. 
The comparative infertility of a stallion may often be 
traced directly to the fact that he is kept stabled in a small 
dark stall with no regular exercise. Mares both before 
and after breeding should be given regular exercise. It 
is better that they should work at some slow regular task 
every day. 

In an investigation on the relation of exercise to the 
development of the internal organs by Kulbs and Ber- 
berrich,^ it was found that in the case of dogs and swine 
the size of the muscles and the weight of the heart and 
liver were increased by exercise. It was also observed 
that the color of the bone marrow was deepened. 

1 " Jahrbuch Wiss. und Prakt. Tierzucht," 6 (1911), p. 232. 



90 THE BREEDING OF ANIMALS 

Darwin ^ reports that " It has been found in France 
that with fowls allowed considerable freedom, only twenty 
per cent of the eggs failed ; when allowed less freedom, 
forty per cent failed ; and in close confinement, sixty out 
of the hundred were not hatched." 

88. The fertility of domesticated animals. — From 
what has already been said regarding confinement and 
its deleterious effect on fertility, it might be concluded 
that domestication is unfavorable to high fertility in 
animals. This is far from the truth. Domestication 
furnishes or ought to furnish the most favorable conditions 
for high fertility in animals. A regular and abundant 
supply of nutritious food, shelter from a rigorous climate, 
and the opportunity for selection by man all contribute 
to the development of a relatively high degree of fer- 
tility in animals. All races of domestic animals are more 
fertile than their wild prototypes. Darwin has pointed 
out that the tame rabbit gives birth to four to eleven in 
a litter and breeds six or seven times a year, while the 
wild rabbit only produces five or six young at one time 
and breeds four times yearly. The domestic fowl may 
produce as many as 200 or more eggs in one year, while 
the female of the wild progenitor of the domestic hen lays 
only six to ten eggs in a year. The same remarkable 
difference exists between the domestic and wild duck. 
The Indian Runner duck under domestication will pro- 
duce 250 eggs a year, and the wild duck only five to ten 
eggs in one year. At the Government Experiment 
Station of New South Wales in Australia, six Indian 
Runner ducks laid 1601 eggs in one year, an average of 
267 eggs each. 

1 Darwin, "Animals and Plants under Domestication," 
vol. IT. 



FERTILITY 91 

89. Age and fertility. — The fertility of animals is 
influenced by age. Young animals that have not yet 
reached maturity are generally less fecund than mature 
individuals. There is also some evidence to show that 
old mature animals are more prolific than younger mature 
animals. It is highly probable that skillful feeding and 
management may result in a significant increase as age 
advances. 

90. Relation of age to fertility in swine. — At the 
Missouri Experiment Station, the author has had under 
investigation the relation of the age of animals to their 
breeding powers. The animals used in this experiment 
have been swine, and the general plan has been to divide 
the sows into three groups according to age. Group I 
is composed of very young sows from four to five months 
of age; group II of half mature sows about eighteen 
months of age ; and group III of mature sows from twenty- 
four to thirty months old. The young immature sows 
of group I have been bred at the first appearance of 
puberty, which in well-fed sows is from four to five months 
old. The female offspring of the immature sows are 
again bred at the first appearance of heat, and this will 
be continued indefinitely. A number of interesting 
phenomena have been observed, but only those results 
which throw light on the relation of age to the fertility 
of the mother are recorded here. 

91. Influence of age of sow on size of litter. — In 
the Missouri experiment described above, there have 
been to date (1913) twentj^-six litters from immature 
sows. The average number of pigs to the litter has been 
four and eight-tenths. From the half mature sows, 
eight litters have resulted in an average of six and three- 
tenths to a litter. The average number of pigs in six 



92 THE BREEDING OF ANIMALS 

litters from the fully mature sows has been six and five- 
tenths. 

The sows used in this experiment were all of the same 
breeding, and received the same care, and the food, shelter 
and all other conditions have been similar. The differ- 
ences observed then must be due to the factor of age. 
It will be observed that there is a marked difference 
between the size of the litters of the immature sows and 
the older ones. The litters of the older sows are materi- 
ally larger than from the immature sows. 

The highest fertility in swine is not reached until the 
mother is at or near maturity. It may not always be 
profitable for the swine-breeder to delay breeding sows 
until full maturity, T^ut it is apparent that when the breed- 
ing herd is composed of older sows, a smaller number 
need be maintained for the production of the pigs needed 
in a given system of farm management. 

Interesting statistics have been compiled by George 
M. Rommel ^ from the records of the American Poland- 
China Record Association, which have an important 
bearing on this point. These statistics include the breed- 
ing records of 6145 sows recorded in 1902. There were 
examined the breeding records of 2010 one-year old sow^. 
The litters of 1520 one-year-old sows, or seventy-five per 
cent, ranged from five to eight pigs. 

The average litter of 2047 two-year-old sows numbered 
seven and five-tenths. The number in each litter of 
1483 sows, or seventy-two per cent, ranged from six to 
nine pigs. 

The average number of pigs in the litters of 1157 
three-year-old sows was seven and nine-tenths. The 
average litter recorded for 606 four-year-old sows was 

1 American Breeders' Association, Report 19. 



FERTILITY 



93 



eight and three-tenths. The records for 325 five-year- 
old sows give the average size of Htter as eight and seven- 
tenths. The total number of sows examined, ranging 
in age from one to five years, was 6145 and the average 
size of litter for the whole number was seven and four- 
tenths. 

The number of animals included in these investiga- 
tions and the unquestioned accuracy of the records make 
these figures valuable. It is clear that the sows increase 
in fertility from one to five years. From the standpoint 
of the practical breeder, it would seem that sows from 
two to four years of age will be most profitable from the 
standpoint of prolificacy. 

92. Relation of age to fertility in sheep. — The greater 
fertility of the older females has been noted in ewes by 
the Wisconsin Experiment Station in Bulletin No. 95. 
Observations made at that station on the percentage of 
increase from ewes of different ages show that two-year- 
old ewes gave an annual increase of 158 per cent, three- 

The Effect of the Age of Ewes on Per Cent of In- 
crease AND Sex op Lambs 

WISCONSIN experiment STATION, BULLETIN 95 



Age of Ewe 


Two 
Years 


Three 

Years 


Four 
Years 


Five 

Years 


Six 
Years 


Seven 
Years 


Bearing 


No. 


Per 
cent 


No. 

30 

58 

6 

75 

72 


Per 
cent 


No. 


Per 
cent 


No. 


Per 
cent 


No. 


Per 

cent 


No. 


Per 
cent 


Single Lambs . 
Pairs Twins . 
Sets Triplets . 
Rams. . . . 
Ewes .... 


62 

72 

4 

96 

100 


44.6 
52.5 
2.9 
49.0 
51.0 


31.9 
61.7 
6.4 
51.0 
44.0 
-S 


21 
42 
6 
71 
53 


30.4 
60.8 

8.8 
57.2 
42.8 


14 
32 
3 
45 
42 


28.5 
65.3 
6.2 
51.7 
48.3 


9 
15 

3 
24 
21 


33.3 
55.5 
11.2 
53.3 

46.7 


6 
3 
1 
10 
5 


60.0 
30.0 
10.0 
66.7 
33.3 


Per cent 
increase . . 


158.0 


174.0 


178.0 


177.0 


178.0 


150.0 



94 THE BREEDING OF ANIMALS 

year-old ewes an increase of 174 per cent, and four- to 
six-year-old ewes an increase of 178 per cent. After 
the age of six years, there w^as a distinct falling off in the 
percentage of increase. 

The foregoing table (page 93) is reprinted entire from 
the Wisconsin bulletin and is interesting as showing the 
distribution of twin and triplet births among the different 
ages and the sex of lambs. 

93. Influence of age of ram on fertility of ewes. — 
The number of young at a birth is generally believed 
to be determined by the number of ova which are ripened 
by the female during any one period of heat. The vigor 
or age of the male used is not generally regarded as hav- 
ing any influence in determining the number born at 
one time. The Wisconsin Station ^ found that during 
a period of six years, the flock of ewes served by a year- 
ling ram produced 150 per cent of lambs. The same 
flock during a similar period of six years was served for 
three of these years by two- and three-year-old rams. 
The average percentage of lambs born from the older 
rams was 180 per cent. The author in discussing these 
results remarks : " These data are quite at a variance 
with the opinion commonly held by sheepmen, generally 
to the effect that a well grown, vigorous yearling ram 
is at his best as a sire. It is also contrary to the belief 
held by many that the vigor of the sire has no apparent 
influence on the percentage of increase." 

94. The effect of the age of poultry parents on the 
offspring. — The general conclusion that fully mature 
animals are more fertile seems to be substantiated by 
the poultry-breeding experiment conducted by Atwood.^ 

1 Wisconsin Experiment Station, Bulletin 95. 

2 Atwood, West Virginia Experiment Station, Bulletin No. 124. 



FERTILITY 



95 













to 




5" 




lO CO 1 CO 


rn 


CO 




CO 
l> 


CO l> 1 t:}5 


to 


00 T*H 




^'^ 


CO 


1-; CO 1 


CO 


CO 
CO CO 




<! 


lO 


c<i d 1 CO 


CO 


l> to 






l> 


T-l 1— 1 lO 


t^ 






^i-" 




00 1 CO 


TJ^ 


to t> 




<1 


o 


rH lO 1 t>I 


CO 


I> (M 






CO 


>— 1 r-l LO 


l> 


1— ( 








l> 












q 1 


"^ 


o 




a( 


I> 


CO 00 1 Oi 


00 


00 CO 


M 




lO 


i-i CO 


CO 








"* 






to 


(3 




^ 1 


CO 


1—1 


« 


d^*^ 


lO 


(N l> 1 CO 


CO 


b- 1-1 


H 




iO 


1— i Tf 


00 


1> 






T— 1 




TtH 




«<^ »H 




<M 1 


00 


CO 




Ph 


1—1 


(M" 00 1 1-1 


1— t 


t> to 






l> 


rH 1—1 lO 


t^ 










CO 




o 




C3 




r-< 


r-i 


to 




Pm 


00 


CO a l^ -rH 


l> 


00 CO 


<N 




00 


T— 1 CO 


o 








(M 




to 


H 


« N 




(M 


to 


l> 


H 


Ph 


(M 


(M lO tH (N 


o 


l> I> 


H 




05 


T— 1 1— 1 CO 


t- 








1—1 




"* 




fl 




t^ 


l> 


CO 




Ph 


Tj< 


1-5 oi 1 CO 


CO 


l> (N 






tH 


1—1 1—1 O 


CO 


1—1 






1—1 














Oi 




t^ 








(N 


1—1 


Tt^ 




Ph 


^ 


Tt^ to Oi O 


1—1 


00 CO 


i-H 




l> 


1— t CO 


00 








00 




th 


fH 


« « 




1—1 


Oi 


to 


H 


Ph 


Oi 


(M OS O O 


to 


1> 00 


H 




t> 


1— I 1—1 CO 


t^ 








to 


00 


CO 
CO 




pL, 


lO 


1-1 00 (M to 


1—1 


l> T-l 






lO 


1— t r^i 


00 


(N 






!=i ■ 5;^ 


■ ' "^ ' J^ 


• M 


JH 1 . . 






-M , ft 






is ■ ' 






M bo 
bi} be 


\£-|^«-2 








&J0 • <D 


. ^ ^ ^ O 


® rJd XJ O • II 






er of e 
bator 
t of 


lbs. 
out i 
ched c 
er of c 
nt hat 


c3 «4-H 
;- O 
o 


100 1 
en fr 
r . 
ieaths 






rQ 3^ 


,^ ^^ -i^ r) O 


■^ rd 


03 c3 c3 ^ 






a ^.^ 


^:§ 










o o 


ft HJ ^ *^ 






^ 



d 
;h 
o 



a 

o 

o 



»o 

1—3 

o 

> 

o 

• l-H 

eg 

• pH 

o 
o 



<D 
<D 
t-l 

pq 
d 

c3 
o 

• 1— ( 

<D 

a 






So o 
WW 



(N CO 



73 
CD d d d 

fn 03 <I> 0) 



96 THE BREEDING OF ANIMALS 

In this investigation, Single Comb White Leghorns were 
employed and a comparison of hens, pullets, two-year 
and three-year-old hens was made. The important results 
may be seen at a glance from the table (page 95). 

The records of this test show that the eggs laid by old 
hens are heavier than those laid by pullets, that the num- 
ber of chicks hatched was ten per cent greater, that the 
initial weight at hatching time, and for several weeks 
thereafter, was greater from the older hens, and finally 
that the percentage of chicks dying from pullet's eggs 
was three times greater than from the mature hens. 

In marked contrast to the above results are those 
published by the Maine Experiment Station in Bulletin 
168. The author (Pearl) of this publication states, 
" The present statistics do not show any marked superi- 
ority of hens over pullets in respect to breeding perform- 
ance, so far as either fertility or hatching quality of eggs 
are concerned." 

95. Age and fecundity. — Duncan ^ distinguishes be- 
tween the ability to bear children, which he calls fecundity, 
from actual productiveness or the number of births, which 
is designated as fertility. From Duncan's investigations 
it is possible to formulate a general law which represents 
a true statement of the relation of age to fecundity. This 
general law has been stated by Marshall ^ as follows : 
" The fecundity of the average individual woman may be 
described, therefore, as forming a wave, which, starting 
from sterility, rises somewhat rapidl}' to its highest point 
and then gradually falls again to sterility." The results 
discussed earlier in this chapter clearly indicate that in 

1 Duncan, "Fecundity, Fertility, Sterility and Allied Topics," 
Edinburgh, 1866. 

2 Marshall, "The Physiology of Reproduction," p. 590. 



FERTILITY 



97 



the case of swine this law is undoubtedly a true statement 
of what actually happens. This law not only applies 
to mammals but is also found in poultry. Geyelin ^ has 
attempted to formulate an average of fertility in poultry 
in relation to age in the following table : 



First Year after hatching . 
Second Year after hatching 
Third Year after hatching . 
Fourth Year after hatching 
Fifth Year after hatching . 
Sixth Year after hatching . 
Seventh Year after hatching 
Eighth Year after hatching 
Ninth Year after hatching . 



15 to 

100 to 

120 to 

100 to 

60 to 

50 to 

35 to 

15 to 

1 to 



20 eggs 

120 eggs 

135 eggs 

115 eggs 

80 eggs 

60 eggs 

40 eggs 

20 eggs 

10 eggs 



These estimates must be regarded as far below the 
performance of well-selected flocks maintained under 
good conditions of food and shelter. The age at which 
pullets begin laying varies greatly, depending upon their 
development. At the Ohio Experiment Station, a White 
Leghorn pullet began laying at four months and fifteen 
days old. At the Missouri Experiment Station Kempster ^ 
reports a White Leghorn pullet beginning to lay at four 
months and nineteen days of age. The number of eggs 
laid by old hens may also greatly exceed the figures given 
by Geyelin. At the Maine Experiment Station a hen 
laid 111 eggs during her ninth year.^ 

A remarkable case of fecundity in sheep is noted by 
Pearl.^ A ewe owned by Barrett for nineteen years 
gave birth to thirty-six lambs which were distributed 
during the breeding life of the ewe as follows (page 98) : 

^ Geyelin, quoted by Marshall, loc. cit., p. 590. 

2 Unpublished records, Missouri Experiment Station. 

^ Maine Experiment Station, Bulletin 266. 

* Pearl, Science, vol. 37, p. 227. 

H 



98 THE BREEDING OF ANIMALS 

LAMBS 

April, 1806 1 

1807 1 

1808 2 

Aprils, 1809 3 

March 29, 1810 3 

Making 6 lambs in 11 months and 26 days 

1811 3 

1812 3 

1813 3 

1814 3 

1815 2 

1816 2 

1817 2 

1818 2 

1819 2 

1820 2 

1821 1 

1822 1 

1823 

1824 _0 

Total 36 

Pearl has further called attention to the fact that 
'^ the median point in the breeding career of this ewe was 
8.17 years. That is, she produced one-half of her offspring 
before and one-half after it." The age of maximum fe- 
cundity in this ewe was 7.34 years. 

96. Nutrition and fertility. — All the physiological 
activities of an animal are influenced by nutrition. This 
is particularly the case with the reproductive functions. 
The fertility of an animal is influenced by the kind and 
the amount of food consumed. Certain kinds of food 
have long been believed to affect injuriously the breeding 
functions of animals. Sugar fed to domestic animals 
in considerable amounts has apparently had an unfavor- 
able influence on fertility.^ Greatly increased activity 

1 Tanner, Journal of Royal Agricultural Society, 1865, p. 267. 



FERTILITY 99 

of the generative organs is characteristic of the spring 
season. At this season most animals, domestic and wild, 
are periodically in heat. This greater activity is un- 
doubtedly due to the abundant supply of nutritious and 
succulent grass. That this kind of food does materially 
influence the fertility of animals is recognized by the 
shepherds of England in the practice of flushing ewes. 
This practice consists in turning the ewe flock on rich 
succulent pastures about two weeks before turning in 
the ram. The flock owners believe that this increases 
the number of lambs and brings the ewes more uniformly 
in heat. The Beinn Bhreagh ^ flock of sheep in Nova 
Scotia belonging to Dr. Bell when fed generously before 
and during the mating season produced a larger number 
of twins. The older ewes also produced a larger per- 
centage of twins. 

97. Excessive food supply and nutrition. — An over- 
supply of nutritious food which causes the animal to 
become abnormally fat is often the cause of sterility 
among the domestic animals. In nature it is rare for 
an animal to remain continuously in an excessively fat 
condition. At certain seasons of abundant food supply 
the wild animal may become fat, but such periods of 
plethora are invariably followed by a scarcity of food, 
and such food must often be gathered by exhaustive 
exercise. Such variations, if not extreme, may be partic- 
ularly favorable for the functioning of the reproductive 
system. Certain it is that the most skillful stockmen 
have long recognized the fact that the female reproduc- 
tive functions are most active when the individual is 
actually gaining in condition. An animal that is main- 
tained in a uniform condition of excessive fatness is not 

^ Bell, Journal of Heredity, vol. V, p. 47. 



100 THE BREEDING OF ANIMALS 

in the best condition for the successful exercise of the 
breeding function. A rapidly improving condition due 
to nutritious food supplied in generous quantities is 
distinctly favorable, provided the animal is not already 
too fat. 

E. Davenport has held that, " excessive food supply 
leads to infertility among both plants and animals.'' 
This is true of long-continued and excessive feeding, but 
a rapidly improving condition of the animal in thin condi- 
tion is distinctly favorable to the highest fertility. It is 
a mistaken idea that starvation or a very limited diet 
is a favorable environment for the successful activity of 
the generative system. Such treatment is only favorable 
in the case of over-fat animals and is oftener the first 
and a very essential step in securing offspring from animals 
that through a long period of overfeeding become tem- 
porarily barren. 

98. Other factors affecting fertility. — A sudden change 
of conditions surrounding the animal, such for example 
as the exportation of an animal from Europe to the United 
States, will often temporarily interfere with the normal 
activities of the reproductive system and the animal 
may be barren for a time. When' the animal has become 
thoroughly accustomed to the changed conditions, its 
breeding powers return and thereafter may function 
normally. Changed conditions may also result in in- 
creased fertility. As shown elsewhere, breeding animals 
in thin condition and existing upon a sparse ration or upon 
a dry dietary, become markedly more fertile when changed 
to richer pastures. 

Some individuals are infertile when mated with cer- 
tain other individuals, but may be fully fertile with others. 
A mare may be sterile when bred to a stallion, but fertile 



FERTILITY 101 

when mated with a jack. Such a physiological aversion 
is not easy to explain, but is nevertheless so frequent as 
to be a well-recognized fact among breeders. Prolonged 
lactation must be regarded as unfavorable to fecundity 
in some species. This is especially true in the case of 
swine, where early weaning of the litter will certainly 
encourage an earlier return of the heat period and thus 
make possible a larger number of litters during the natural 
breeding life of the mother. 

99. Relation of number of mammae in swine to fertility. 
— An interesting study of the mammae in swine was 
reported by Wentworth.^ From these researches there 
is little evidence in favor of the popularly accepted opinion 
that there is a relation between the fertility of swine and 
the number of mammse. The normal type of mammary 
pattern in swine consists of regularly placed pairs on the 
ventral side of the body. The first pair lie immediately 
behind the juncture of the ribs and sternum. The 
greatest variation occurs in the second pair. The last 
pair are closer together and thus nearer the median line 
in an inguinal position. Variations occur in the number 
of pairs and also in the suppression of one nipple of a 
pair. These variations are often inherited. The normal 
number of mammse in the Tamworth and Berkshire 
breeds is 13, 14 and 15, in the Duroc-Jersey breed 10, 
11 and 12. The tendency to vary is greater when the 
number of pairs exceeds five. 

100. Twins. — The normal number of young in several 
of the larger breeds of the domestic animals and in man 
is one. The production of a larger number at a single 
birth is exceptional. It happens, however, that twins 
are frequently born, while triplets and even four and 

1 Wentworth, Amer. Naturalist, vol. 47, p. 257. 



102 THE BREEDING OF ANIMALS 

five at a birth have been reported. When twins are 
born they are either of identical sex or one a male and 
the other a female. In some cases the twins are very 
much alike in all other characters as well as sex. Such 
twins were called by Galton identical twins. It is also 
true that twins are often born which have no greater 
resemblance to one another than ordinary brothers and 
sisters. Such twins undoubtedly develop from separate 
eggs and are known as ordinary or fraternal twins. They 
do not necessarily resemble one another more closely 
than brothers and sisters of the same family except 
that they are of identical age and for this reason might 
be expected to have a closer resemblance than brothers 
or sisters of widely different ages. Fraternal twins may 
be of different sex. Identical twins are believed to come 
from one egg after fertilization. They are always of the 
same sex and very much alike in external and internal 
character and in mental and moral tendencies. 

101. Characters correlated with fertility. — It is in the 
highest degree desirable that the breeder should be able 
to distinguish those qualities, external and internal, 
which are in any way correlated either with fertility or 
sterility. Unfortunately we cannot now speak with as- 
surance on all the supposed evidences of fertility in 
animals, but some characters are undoubtedly closely 
correlated with fertility and we may through them learn 
to judge of the probable existence or nonexistence of 
this most desirable trait. Manifestly, characters closely 
correlated with fertility will finally persist and become 
dominant. It is equally evident that those characters 
of the animal body which are correlated with infertility 
will ultimately disappear. The skillful judge of breed- 
ing animals recognizes some such correlation in the selec- 



FERTILITY 103 

tion of both male and female individuals. The breeder 
emphasizes the existence of those general qualities which 
give to the male a distinctly masculine appearance and 
to the female a clearly recognizable character of femininity. 
The bull possessing a markedly masculine aspect is held 
to be a '' good breeder." Whether it is meant by this 
that such a bull is prepotent in fixing his own charac- 
teristics upon his offspring or, what is more probable, 
that a bull of this character is more than ordinarily effi- 
cient in the development of sperm-cells, it is still true 
that the masculine type may be regarded as in some 
degree at least correlated with fertility. Supernumerary 
mammae have been found in many cases associated with 
exceptional fertility. In describing the dam of triplet 
calves. Pearl ^ remarks : " It is of interest to note that 
this cow has two very small posterior mammae. It is 
of course impossible to say whether this occurrence of 
supernumerary mammse is directly connected with the 
high degree of fecundity exhibited by this cow, but this 
may fairly be regarded as probably the case because of 
the fact that these two things are known to be associated 
in other forms." The sheep breeding experiments at 
Beinn Bhreagh^ by Alexander Graham Bell have suggested 
a possible correlation between extra nipples and unusual 
fecundity. Stature and fertility have been found by 
Pearson ^ to be somewhat closely correlated among women. 
The taller women are on the average more fertile. If this 
is generally true, the stature of women is likely to increase 
at least until it has reached a point which satisfies the 
correlation existing. Among swine-breeders it is generally 

1 hoc. cit. 

2 Bell, Science, N. S., vol. 36, pp. 378-384. 

^ Pearson, "Grammar of Science," pp. 441-445. 



104 THE BREEDING OF ANIMALS 

believed that sows with rather long bodies are more fertile 
than shorter, more compact individuals. It seems to be 
true also that females having a somewhat loose and open 
conformation are generally more certain breeders. 

The milking function of animals is in a measure corre- 
lated with the quality of fecundity. Breeds of animals 
and individuals which have the milking function well 
developed are more fecund than those in which the devel- 
opment of this quality has been neglected. Tanner/ 
in his interesting discussion on " The Reproductive 
Powers of Animals," says : " The formation of milk is 
intimately correlated with the reproductive powers. 
The secretion of milk is dependent upon the activity of 
the mammary glands and these are either under the direct 
influence of the breeding organs or else they sympathize 
very closely with them. Those animals which breed 
with the least difficulty yield the best supplies of milk 
and produce the most healthy and vigorous offspring." 
He also adds that, " Since a short supply of milk is indica- 
tive of and associated with enfeebled breeding powers 
every care should be taken to obviate this defect." 

It must be admitted that our knowledge on the sub- 
ject of characters correlated with fertility is as yet frag- 
mentary and indefinite. The importance of this quality 
in practical breeding should make this a fruitful field 
for further investigation. 

102. In-breeding and fertility. — Continuous in-breed- 
ing among domestic animals has in many instances been 
followed by low fecundity or absolute sterility. It is 
generally believed by practical breeders that of all the 
ill effects supposed to result from in-breeding, lessened 

^Tanner, "The Reproductive Powers of Animals," Journal 
of Royal Agricultural Society, 1865, p. 270. 



FERTILITY 105 

fertility is the one most likely to follow. Whether this 
loss of fecundity in animals of consanguineous breeding 
is to be attributed to in-breeding per se or whether it is 
due to the rapid fixing of a tendency to sterility already 
existing in the family, it is nevertheless true that there 
exists a certain amount of probability that continuous 
close-breeding will ultimately affect injuriously the 
fertility of animals. This question is discussed at some 
length under " In-breeding/' Chapter XL 

103. Cross-breeding and fertility. — It naturally fol- 
lows that if in-breeding is unfavorable to full fecundity, 
cross-breeding must tend to develop this desirable quality. 
Here again it is not easy to trace the increased fertility 
which follows the mating of animals of diverse characters 
to the sole act of crossing. Many of the cases of increased 
fecundity due to crossing may be explained on the basis 
of introducing the new quality of high fertility. If fertil- 
ity is a dominant character transmitted in accordance 
with the Mendelian principle of dominance, it is easy to 
understand why the cross-bred animal may exhibit, as 
it often does, a greater degree of fecundity than can be 
accounted for on the assumption of blended inheritance 
of this quality from both parents. What actually happens 
is that one of the parents possesses the quality of fertility 
in high degree and this becomes dominant in the offspring. 
A certain proportion of the offspring, therefore, receive 
in the constitution of the germ-plasm all- the high fertility 
which is an inherent part of the germ substance of the one 
parent. It should also follow that a certain proportion of 
the offspring inherit unchanged the tendency to low fecun- 
dity characteristic of the other parent. It must be ad- 
mitted that evidences of the latter are still lacking, but it 
should be possible by experiment to determine this point. 



106 THE BREEDING OF ANIMALS 

104. Unusual fertility. — Each species and most varie- 
ties or breeds of animals have a fairly uniform and normal 
rate of increase. Thus the normal number of young at a 
birth in cattle and horses is one. It is also probably 
true that among sheep one is the normal number of young 
at each birth. But many breeds of sheep have been 
so changed by domestication that twins are frequent 
and triplets are not rare. The quality of fertility is 
undoubtedly transmitted by heredity. It is therefore 
possible to increase the normal fertility of the domestic 
sheep by selection. Among cattle the production of 
twins has not been regarded as a particularly desirable 
quality, and hence no attempt has been made to increase 
the normal birth number of the bovine species. It is 
not difficult, however, to conceive that it would be com- 
paratively easy to develop a breed or variety of cattle 
which would produce twins. Cases of unusual fertility 
among all classes of the domestic animals are frequent. 
These are of enough importance from a practical point 
of view and of sufficient biological significance to be given 
a place in a discussion on fertility. 

105. Unusual fertility among horses. — Exceptional 
fertility among horses is generally to be found in connec- 
tion with longevity and active and regular functioning 
of the breeding powers rather than in unusual numbers 
of young at a birth. A mare twenty-five years old, owned 
by R. O'Heren of Illinois, in 1904 was suckling her twen- 
tieth colt. She was one-half Thoroughbred and one-half 
Clydesdale and was still strong and active.^ The Thor- 
oughbred mare, Fanny Cook, dam of Daniel Lambert, 
produced fifteen foals and dropped twins at twenty-two 

1 Reported in a letter to the author by R. H. Dunn, Illiopolis, 
111. 



i 



FERTILITY 107 

years of age. A Clydesdale mare belonging to G. W. 
Henry of Burlington, Iowa, was the mother of nine- 
teen foals and was supposed to be in foal again.^ Poca- 
hontas, a running mare, was the mother of fifteen foals 
and dropped her last ' at the time she was twenty-five 
years of age. 

106. Unusual fertility among cattle. — Some remark- 
able cases of fecundity among cattle have been recorded. 
In most cases the ability to ripen a number of eggs dur- 
ing one period of heat seems to be inherent. A cow that 
has produced twins or triplets is very apt to do so again. 
This tendency to multiple gestation in cattle is well 
illustrated by a family of cattle on a New Hampshire 
farm reported by Wentworth.^ " The foundress of the 
family was a grade Holstein cow, herself a twin, about 
seven years old. She has been on the farm ever since 
she was dropped and has given birth to seven calves. 
Her first service was to a Guernsey bull and resulted in a 
pair of yellow and white heifers, one of which is now in 
the herd. Her second mating to a red Shorthorn bull 
resulted in a single black and white bull calf that was 
vealed. An Ayrshire bull sired her third calves, twin 
black and white bulls, but neither of these was good 
enough to raise. Her fourth service was to a Holstein 
bull and from it she produced twin black and white heifers 
that promise well as milkers." 

"The yellow and white twin first produced by the 
old cow is now four years old and has twice borne twins. 
To an Ayrshire bull she produced a pair of yellow and 
white bull calves that early went to the butcher and to a 

1 Sanders, "Horse Breeding," p. 179. 

2 Wentworth, E. N., " Twins in Three Generations," Breeder's 
Gazette, vol. 62, p. 133. 



108 THE BREEDING OF ANIMALS 

Holstein bull she gave birth to twin black and white 
heifers last December." 

Pearl ^ has described an interesting case of triplet 
calves from a grade Guernsey cow seven years old. The 
sire was a young grade Hereford bull which had not 
shown any unusual tendency to sire twins or triplets. 
Two of the .calves were heifers and had the typical white 
face of the Hereford breed. The third calf, a bull, was 
a typical Guernsey and in color and coat markings re- 
sembled somewhat closely his dam. (Plate IV.) 

In reference to the breeding record of these triplet 
calves, Pearl says : " The writer asked Mr. Walter, 
the owner of the calves here described, to pay particular 
attention to the sexual behavior of these triplets. This 
was done. As has already been implied in what has gone 
before, the male individual of the triplets was entirely 
functional sexually. He was used in service locally; 
got good calves ; and apparently got as high a proportion 
of calves as would be expected from a bull of his age. In 
regard to the sexual history of the female individuals 
of the triplets, Mr. Walter has the following to say in a 
letter dated April 11, 1910. After noting the fact that 
these two supposed heifers had been killed and sold in 
the village market he says : ' Neither of them had 
ever been in heat.' In earlier letters Mr. Walter on sev- 
eral occasions said that these calves never showed the 
slightest signs of being in heat. From the account given 
by the butcher who killed these animals it appears prob- 
able that in both individuals the conditions were such as 
have been described for many free-martins. Neither 
uterus or tubes were recognized, but the vagina apparently 

» Pearl, "Triplet Calves," Bulletin 204, Maine Agricultural 
Experiment Station. 





Plate IV. — Unusual fertility in the cow. 
grade Guernsey dam and grade Hereford sire. 



Triplet calves from a 



FERTILITY 109 

ended at its anterior end as a blind sack. Although 
detailed anatomical data are lacking, there can be 
little doubt, I believe, because of both physiological 
fact and absence of oestrus and the lack (?) or minute, 
infantile condition of uterus and Fallopian tubes, that 
these two supposed female individuals were really free- 
martins." 

The cow possessed two supernumerary mammae just 
behind the posterior pair. The occurrence of super- 
numerary mammae has before been observed to accom- 
pany the tendency to multiple births. 

A seven-year-old Shorthorn cow dropped seven dead 
calves at one birth. They were sired by a Holstein bull.^ 
A Shorthorn cow three years old, on post mortem, was 
found to be carrying six perfectly developed calves in 
her uterus.^ Another Shorthorn cow gave birth to four 
calves, three of which were weak and undeveloped.^ A 
cross-bred cow gave birth to seven calves within a period 
of twelve months. All these calves w^ere born alive.^ 
A cow dropped three pairs of twins in succession during 
a period of two years.^ A grade Guernsey cow on a farm 
in Washington County, Pennsylvania, gave birth to 
triplets. This cow was ten years old and had produced 
fifteen calves at eight births. A cow twenty-two years 
old is reported as having had twenty calves and was 
again pregnant.® A remarkable case of continued high 
fertility in a cow is quoted by Pearl from McGillwray's 
" Manual of Veterinary Science and Practice." The cow 

1 Country Gentleman, 1895, p. 595. 

2 Ibid., 1880, p. 313. 

3 Ihid., 1891, p. 339. 

4 Ibid., 1893, p. 231. 

5 Breeder's Gazette, 1898, p. 7. 

^ Rural New-Yorker, 1906, December. 



110 



THE BREEDING OF ANIMALS 



described was of " the black polled breed " and her 
record of births follows : 



Year Number of Calves at Birth 



1842 






1 


1843 






3 


1843 






4 


1844 






2 


1845 






3 


1846 






6 


1847 






2 


1848 






4 


Total 






25 



This the cow's first calf 

All lived to adult age 

One died. (Seven calves in one year) 

Lived to maturity 

Lived to maturity 

All died prematurely 

Came to maturity 

Mean number per birth — 3.125 



107. Unusual fertility among sheep. — Sheep normally 
produce a larger proportion of twins than cattle or horses. 
This may be due in a measure to the fact that the sheep 
has a much shorter period of gestation. It is true in 
general that those mammals having the shortest periods 
of gestation are most prolific. Some remarkable cases 
of great fertility among sheep are matters of record. 
A three-year-old grade Cotswold ewe gave birth to five 
fully developed lambs. Two died at birth, the others in 
a few hours.^ A Horned Dorset ewe four years old 
dropped five lambs at two births within a ten months' 
period.^ A Radnor ewe dropped six lambs at one birth, 
of which five lived and thrived.^ An Oxford-down ewe 
gave birth to four strong, vigorous lambs which grew 
rapidly and weighed one hundred and sixty-two pounds 
at eight weeks old.^ A prolific ewe at one birth dropped 
five lambs, all of which were perfectly developed and grew 
rapidly.^ A Leicester ewe gave birth to six strong, healthy 

1 Country Gentleman, 1893, p. 171. 

2 Breeder's Gazette, 1894, p. 327. 

^ Country Gentleman, 1892, p. 331. 
" Breeder's Gazette, 1893, p. 388. 
^ Country Gentleman, 1878, p. 329. 



FERTILITY 111 

lambs, four of which the mother nursed successfully. 
The earless Shanghai breed of sheep exhibited in the 
London Zoological Gardens in 1857 seem to have inherited 
a remarkable fecundity. Bartlett ^ has described this 
variety as breeding twice each year and often producing 
four or five at a birth. In the spring of 1857 three ewes 
of this breed gave birth to thirteen lambs. 

108. Unusual fertility among swine. — There is more 
difficulty in determining the normal number of young at 
a birth among swine than among other domestic animals. 
There is considerable variation among individuals belong- 
ing to the same breed and between different breeds. 
Some particular cases of high fertility are described 
below : 

A three-year-old Chester White sow ^ farrowed ninety- 
six pigs in six litters. There were fourteen in each of 
the first three litters and eighteen in each of those last 
farrowed. This tendency among highly fecund indi- 
viduals to give birth to larger and larger numbers has 
been observed in cattle, sheep and swine. 

A Poland China sow ^ produced thirty-four living pigs 
in three litters during a single twelve months' period. 

A sow ^ gave birth to twenty-one pigs in a litter. Pre- 
vious to this she had farrowed two litters of fifteen and 
seventeen pigs each. A sow of uncertain breed ^ dropped 
twenty-three pigs in one litter. All but two of these 
were born alive. The same sow gave birth to eighty- 
five pigs in five litters. Ray L. Zimmerman of Amazonia, 
Andrew County, Missouri, reports to the author that a 

1 Bartlett, Proc. Zool. Soc, London, 1857, p. 105. 

2 Breeder's Gazette, 1897, p. 368. 

3 Ibid., 1894, p. 308. 

^ Country Gentleman, 1887, p. 281. 
5 Ibid., i894, p. 915. 



112 THE BREEDING OF ANIMALS 

Poland China sow owned by W. Minner of that county 
farrowed twenty-five pigs in one litter. 

109. Unusual fertility among poultry. — An instance 
of remarkable ability in egg-laying is given in the Experi- 
ment Station Record, vol. 28, p. 270. In this volume is 
described a Single Comb Brown Leghorn hen which laid 
257 eggs in twelve months. This hen weighed only 
three and two-tenths pounds. The average weight of 
the eggs was one and eight-tenths ounces. At the Dela- 
ware Experiment Station a White Leghorn hen, Lady 
Eglantine, laid 314 eggs in one year. 



CHAPTER VI 
STERILITY 

It goes without saying that the first essential quaUty 
in a breeding animal is the ability to produce young. 
The more highly developed the animal is in those special 
characters which have been fixed by selection, the more 
important becomes the mere ability of an individual to 
give birth to offspring. In an animal reared primarily 
for commercial purposes, like the hog or the beef type, 
the barren individual is not so serious a loss, as it may 
still have a value for meat. 

It is well known that many individuals among the 
domestic animals are sterile. Such sterility is found 
among animals reared under the best conditions, as well 
as among those subjected to less skillful husbandry. 
Barrenness occurs in individuals which are a part of 
herds or flocks in which all animals are surrounded by 
identically the same conditions. It must be true, there- 
fore, that some animals possess a tendency to barrenness 
in a more marked degree than others. This tendency 
may possibly be inherited. Barrenness may be only 
temporary or it may be a permanent condition. When it 
is a temporary condition, it can often be alleviated by 
knowing the conditions which are favorable to fertility, 
and particularly those conditions which are known to act 
unfavorably upon the breeding functions. 
I 113 



114 THE BREEDING OF ANIMALS 

110. The causes of sterility. — The various causes ^ 
of sterility may be classified as anatomical, physiological, 
pathological or psychological. Sterility in the male may 
be due to an inability to perform the sexual act, which 
condition is known as impotence, or it may be due to an 
inability properly to develop spermatozoa. 

111. Causes of sterility in the male. — The male may 
be sterile as a result of undeveloped testicles as in some 
ridglings, where the testicles are retained in the abdomen. 
The ridgling is not always permanently sterile and may 
be fully fertile, but the failure of the testicles to descend 
normally from the abdominal cavity into the scrotum 
is to be regarded with suspicion by the breeder. The 
only way to determine whether a particular ridgling is 
fertile is by actual trial. There is no medicinal or surgi- 
cal treatment which can make a barren ridgling fertile. 

Bulls, boars and stallions which are fed upon a generous 
ration of highly nutritious food and are not given regular 
exercise tend to become over-fat, and such a condition 
often leads to fatty degeneration of the testicles and conse- 
quent sterility. This condition is recognized by all suc- 
cessful breeders. Breeding males that have proven 
themselves of great merit as sires and are not intended 
for exhibition are generally and wisely maintained on a 
moderate allowance of nutritious food, being careful 
to limit the amount and provide some means for exercise, 
thus avoiding the almost inevitable fatty degeneration 
of the reproductive tissues which follows long-continued 
high feeding combined with little exercise. An example 
of the intimate relation of these factors to fertility is to 
be observed in the breeding practices of many modern 

^ See "Diseases of the Horse," U. S. Department of Agri- 
culture, 1907, pp. 151-154. 



STERILITY 115 

owners of draft stallions as compared with the methods 
of early stallioners in the newer agricultural sections of 
the United States. It was formerly the custom to drive 
or ride the stallion from farm to farm, thus often covering 
a territory of 100 to 200 square miles. Stallions so handled 
were notoriously sure foal-getters and not infrequently 
were successful in getting from eighty-five to ninety-five 
per cent of the mares in foal. The modern plan of 
keeping the draft stallion in high condition and stand- 
ing him for service at one barn, thus requiring all mares 
to come to him, has undoubtedly reduced the fertility 
of draft stallions. It is no unusual event for k draft 
stallion so managed to get only sixty per cent of mares in 
foal, while seventy-five per cent of the mares in foal is 
regarded by some stallioners as a fair average for stal- 
lions handled in this manner. The fatty degeneration 
of the vasa deferentia or excretory ducts of the tes- 
ticles is also a not infrequent cause of sterility in very 
fat animals. 

Any injury or deformity of the penis which renders 
the act of copulation painful or impossible is to be included 
in the category of anatomical causes of sterility. In 
this class may be included inflammation or ulceration 
of the mucous membrane enclosing the penis, paralysis 
of that organ, and the presence of tumors on the penis 
itself or its appendages. Muscular and bone diseases 
which in any way interfere with the exercise of the breed- 
ing function are causes of barrenness. Spavin or ring 
bone may cause the stallion such inconvenience and dis- 
tress in mounting as to prevent copulation and thus indi- 
rectly be a cause of barrenness. Similarly, diseases of the 
muscles of the back and loins may be responsible for 
sterility in certain individuals. Diseases of the brain 



116 THE BREEDING OF ANIMALS 

and spinal cord, particularly those which control the 
act of coition/ diabetes and albuminuria are to be regarded 
as causes of sterility. 

The potency of the semen of the male may be so weak- 
ened by too frequent services by the stallion as to result 
•in sterility. The number and frequency of services 
which can be required of a stallion and still retain the 
full vitality of the sperm-cells varies greatly with different 
individuals. An interesting contribution to this subject 
is reported by Lewis : ^ A draft stallion was permitted 
one cover daily for nine consecutive days. Samples 
of the semen were taken to the laboratory in a warm steri- 
lized receptacle. The number of sperm-cells to the cubic 
millimeter in the semen from the first service was 131,750. 
The number of sperm-cells decreased daily with consider- 
able uniformity until the ninth service, when the number 
suddenly diminished from 51,480 to 5840. The vitality 
of the spermatozoa was determined by maintaining the 
fluid at a uniform temperature and determining the num- 
ber of viable sperm-cells at the end of a given period. 
Thus when the semen was kept at a temperature of 31 
to 35° C. it was found that five per cent of the 
cells from the first service were alive after nine and five- 
tenths hours. From the third service no cells were alive 
after six hours. From the sixth service no cells were 
alive after four hours, and from the eighth service no cells 
were alive after three hours. In a second test a grade 
stallion was bred eleven times on consecutive days. 
The author summarizing this test concludes that : ^ 
" Approximately the vitality of the cells decreased one- 

1 Comer, "Diseases of the Male Generative Organs, " 1907. 

2 Lewis, Oklahoma Experiment Station, Bui. 96, 1911. 
^ See Marshall, "The Physiology of Reproduction." 



STERILITY 117 

half and the number to one-fifth in the last or eleventh 
service of the series as compared with the condition of 
the semen at the first service." Other conditions which 
are to be regarded as sources of barrenness are incomplete 
erections, premature ejaculations, fear and repugnance. 
The inability of the male to produce fertile semen may 
be a congenital condition or it may be acquired through 
some of the causes mentioned in this chapter. 

112. Sterility in the female. — The failure of the 
female to produce offspring is due to a variety of causes. 
Some of these are inherent and cannot be successfully 
treated. Such animals are permanently barren and of 
course useless for breeding purposes. There are other 
causes of infertility which are the result of purely tempo- 
rary circumstances, and these may often yield to skillful 
treatment by man and valuable animals thus become 
regular breeders. Some of the more important causes 
of sterility which are temporary and which may yield 
to treatment are mentioned below. 

113. Closure of the cervix. — Mares and cows often 
fail to become pregnant as a result of the constriction of 
the muscles forming the neck of the womb. This spas- 
modic closure of the cervix prevents the passage of the 
semen from the vagina into the uterus, and the fertiliza- 
tion of the egg is thus prevented. This condition is more 
frequent in young females that have never been pregnant, 
but is not uncommon among animals that have previously 
given birth to offspring. This condition may generally 
be successfully treated by a simple operation known to 
the stallioners as opening. The treatment for this con- 
dition is admirably and clearly described by Law ^ as 
follows : '' Spasmodic closure of the neck of the womb 

^ " Diseases of the Horse," U. S. Department of Agriculture, 1907. 



118 THE BREEDING OF ANIMALS 

is common and is easily remedied in the mare by dilata- 
tion with the fingers. The hand, smeared with bella- 
donna ointment and with the fingers drawn into the form 
of a cone, is introduced through the vagina until the pro- 
jecting, rounded neck of the womb is felt at its anterior 
end. This is opened by the careful insertion of one finger 
at a time, until the fingers have been passed through the 
constricted neck into the open cavity of the womb. The 
introduction is made with a gentle rotary motion, and 
all precipitate violence is avoided, as abrasion, laceration 
or other cause of irritation is likely to interfere with 
the retention of the semen and with impregnation. If 
the neck of the womb is rigid and unyielding from the 
induration which follows inflammation — a rare condi- 
tion in the mare, though common in the cow — more 
force will be requisite, and it may even be needful to incise 
the neck to the depth of one-sixth of an inch in four 
or more opposite directions prior to forcible dilation. The 
incision may be made with a probe-pointed knife, and 
should be done by a professional man if possible. The 
subsequent dilatation may be best effected by the slow 
expansion of sponge or seaweed tents inserted into the 
narrow canal. In such cases it is best to let the wounds 
of the neck heal before putting to horse." 

114. Obstruction of Fallopian tubes resulting from 
excessive fatness. — In excessively fat animals, the 
Fallopian tubes may become mechanically obstructed 
by the pressure of fat tissue. This closure of the tube 
makes it impossible for the ova to descend into the uterus, 
and although the female may come regularly in heat and 
coition occur, the animal does not become pregnant. 
This condition does not necessarily involve fatty degen- 
eration of the reproductive tissues, but may be associated 




Plate V. — Normal healthy uterus of sow. a, ovary ; h, fimbriated 
end of Fallopian tube ; c, central part of Fallopian tube ; d, junction of 
Fallopian tube with horn of uterus ; e, uterine folds of the horns of uterus ; 
/, body of uterus; o, position of *'os uteri"; vag., vagina vulva, bladder. 




Plate VI. — Sterility in the sow. Generative organs of a domestic 
sow, illustrating cystic ovaries which in this case resulted in complete 
sterility. 



STERILITY 119 

with it. It is of course not possible to determine by 
external examination of the live animal whether failure 
to breed in a particular case is due to mechanical obstruc- 
tion of the Fallopian tubes or to other causes. It is often 
possible to overcome this difficulty by dieting the animal. 
Very fat animals which do not breed should be placed 
upon a restricted diet which will cause them to lose weight 
regularly until they have regained a normal breeding 
condition. 

115. Other causes of barrenness. — Other conditions 
which may be regarded as more or less temporary causes 
of barrenness are : (a) insufficient food supply, causing 
emaciation and a consequent failure of the sexual organs 
to mature ova; (6) failure of the animal to retain the 
semen of the male, due to unusual nervous irritability 
of the female sexual organs ; and (c) sudden and marked 
change of condition, such as is brought about by the 
transportation of animals from one continent to an- 
other. (Plates V and VI.) 

Some of the causes and treatment of sterility have 
already been somewhat fully discussed under the general 
subject of fertility. A mere mention of some of the 
above causes of sterility indicates the treatment. In 
many cases of sterility all that is needed is to remove 
the cause. The nervous irritability of the female sexual 
organs seems to be caused by, or at least associated with, 
an unusual flow of blood to the generative organs, causing 
congestion. This condition can be alleviated sometimes 
by exercising the female even to the point of exhaustion. 
It is a well-known fact that the Arabs were in the habit 
of riding their mares to exhaustion just before mating 
with the stallion. This treatment brought about a 
generally relaxed condition of the whole body and par- 



120 THE BREEDING OF ANIMALS 

ticularly of the reproductive organs, which is to be re- 
garded as favorable for conception. 

The importation of animals from foreign countries 
often results in temporary barrenness. This condition 
seldom or never becomes permanent. 

116. Sterility from fatty degeneration. — The main- 
taining of animals in an excessively fat condition for a 
long period of time will eventually result in fatty degener- 
ation of the tissues. When this condition attacks the 
ovaries, it frequently causes permanent sterility. Cer- 
tain foods are believed to hasten fatty degeneration of the 
reproductive tissues. Tanner ^ holds that " this fatty 
degeneration of the ovaries has been traced to the use of 
foods rich in sugar. I have reason to believe that the 
action of sugar in its various forms is most important 
in its influence upon the generative system, and I think 
there is just cause for considering that any animal may 
by its use be rendered incompetent for propagating its 
species." 

117. Sterility caused by abortion. — Among the impor- 
tant causes of infertility among the domestic animals 
probably none is responsible for so many failures to 
produce living offspring as abortion. Two kinds of 
abortion are recognized, non-contagious and contagious. 
Non-contagious abortion may result from a variety of 
causes closely associated with the environment of the 
animal. Law ^ gives a number of the more important 
causes of abortion in the mare. " The mare may abort 
by reason of almost any cause that very profoundly dis- 

^ Tanner, "The Reproductive Powers of the Domestic Ani- 
mals," Journal of the Royal Agricultural Society, vol. 1, 1865, 
p. 267. 

2 Law, "Diseases of the Horse," U. S. Department of Agri- 
culture, 1903. 



STERILITY 121 

turbs the system. Hence very violent inflammations 
of important internal organs (bowels, kidneys, bladder, 
lungs) may induce abortion. Profuse diarrhea, whether 
occurring from the reckless use of purgatives, the con- 
sumption of irritants in the food, or a simple indigestion 
is an effective cause. No less so is acute indigestion 
with evolution of gas in the intestines (bloating). The 
presence of stone in the kidneys, uterus, bladder or urethra 
may induce so much sympathetic disorder in the w^omb 
as to induce abortion. In exceptional cases wherein 
mares come in heat during gestation, service by the 
stallion may cause abortion. Blows or pressure on the 
abdomen, rapid driving or riding of the pregnant mare, 
especially if she is soft and out of condition from idleness, 
the brutal use of the spur or whip, and the jolting and 
straining of travel by rail or boat are prolific causes. 
Bleeding the pregnant mare, a painful surgical opera- 
tion, and the throwing and constraint resorted to for an 
operation are other causes. Traveling on heavy muddy 
roads, slips and falls on ice, and jumping must be added. 
"The stimulation of the abdominal organs by a full drink 
of iced water may precipitate a miscarriage, as may expo- 
sure to a cold rainstorm or a very cold night after a warm 
day. Irritant poisons that act on the urinary or genera- 
tive organs, such as Spanish flies, rue, savin, tansy, cotton- 
root bark, ergot of rye or other grasses, the smut of 
maize and other grain, and various fungi in musty fodder 
are additional causes. Frosted food, indigestible food 
and, above all, green succulent vegetables in a frozen 
state, have proved effective factors, and filthy stagnant 
water is dangerous. Low condition in the dam and 
plethora have in opposite ways caused abortion, and hot, 
relaxing stables and lack of exercise strongly induce it. 



122 THE BREEDING OF ANIMALS 

The exhaustion of the sire by too frequent service, entail- 
ing debility of the offspring and disease of the fetus or of its 
envelopes, must be recognized as a further cause." The 
symptoms of abortion are similar to those of approach- 
ing parturition (see p. 75), if the threatened abortion 
occurs during the later stages of pregnancy. Abortion 
may occur during the first four weeks of pregnancy with- 
out any very marked symptoms. The fact of abortion 
is indicated by the animal again coming in heat. But, 
as already shown in cases of superfoetation, the occurrence 
of heat is not absolute evidence that abortion has resulted. 
Ewart ^ has called attention to the fact that the mare 
is far more apt to abort at certain stages of gestation 
than at others. He regards the period from the sixth 
to the ninth week as one during which the mare is pecul- 
iarly susceptible to changes in her environment which 
may have a tendency to cause abortion. This is due 
to a change in the form of attachment of the foetus to the 
uterus, from the primitive yolk sac to the more permanent 
villi. " At the end of the third week of gestation, when 
the reproductive system passes through one of its periods 
of general excitement, about one-fourth of the embryonic 
sac probably adheres to the uterus ; but at the end of the 
sixth week, when another wave of disturbance arrives, 
all the grappling structures are at one pole. Hence, 
there is probably more chance of the embryo ' slipping ' 
at the end of the sixth than at the end of the third week. 
About the end of the seventh week the supply of nourish- 
ment by means of the yolk sac is coming to an end, and 
there is, perhaps, still about this time an hereditary tend- 
ency for the embryo to escape. Unless the new and more 
permanent nutritive apparatus is provided, unless a 

1 Ewart, quoted by Marshall, loc. cit., p. 615. 



STERILITY 123 

countless number of villi rapidly sprout out from the 
allantois, the embryo will die from starvation during 
the eighth week, and in a few days be discharged. It 
may, therefore, be taken for granted that there is a cer- 
tain amount of danger at the end of the third and sixth 
weeks, but that the most critical period is about the end 
of the seventh or beginning of the eighth week ; for unless 
the villi appear in time, and succeed in coming into suffi- 
ciently intimate relation with the uterine vessels, the 
developmental process is of necessity forever arrested." 

Abortion among sheep seems to be largely due to debili- 
tating conditions due to insufficient and unsuitable food, 
although Heape ^ has pointed out that shearling ewes 
are more apt to abort than those of maturer age. 

118. Contagious abortion and sterility. — The most 
insidious, widespread and generally important cause of 
sterility, especially among cows, is due to a germ infection 
(Bad. abortus) which is recognized under the terms con- 
tagious or infectious abortion. It is found oftener in 
herds of dairy cattle than among beef breeds, not because 
dairy animals are more susceptible to this disease, but 
because they are generally handled in such a manner as 
to provide more favorable conditions for its spread. 
Beef breeds are generally less closely housed and they 
are more frequently permitted to calve on the pastures, 
thus avoiding two common circumstances favorable for 
the transmission of the disease. The infection is carried 
chiefly by the bull. If a healthy bull is permitted to 
serve a cow infected with the germ of abortion, he will 
generally transfer the infection to all cows which later 
may be served by him. The disease is not communicated 
to any important extent from cow to cow by merely 

1 Heape, "Abortion, Barrenness and Fertility in Sheep." 



124 THE BREEDING OF ANIMALS 

standing side by side in the same barn. The Scottish 
Committee appointed to investigate abortion found that 
infection might be carried from a diseased cow to a healthy 
animal by inserting a small wad of cotton into the vagina 
of a diseased cow for twenty minutes and transferring 
this to the vagina of a healthy pregnant cow or sheep. 
Such infection invariably caused abortion within a month.^ 
The specific organism Bacterium abortus is probably not 
the only germ which may cause abortion. MacFadyean ^ 
has called attention to the very great increase in the 
sterility of cows in Prussia and Switzerland during recent 
years. The cause of this sterility has been ascribed to a 
disease known as '' infectious granular vaginitis." This 
affection produces an acute inflammation of the vulva 
and vagina and the infection is spread through a herd 
by the bull. Law ^ holds " that any micro-organism 
which can live in or on the living membrane of the womb 
producing a catarrhal inflammation, and which can be 
transferred from animal to animal without losing its 
vitality or potency is of necessity a cause of contagious 
abortion." 

119. Treatment for contagious abortion. — The con- 
tinuance of contagious abortion is generally prolonged 
even under the best of circumstances. Treatment may 
sometimes be very successful, and again any form of treat- 
ment may fail to make any lasting impression upon the 
disease. As the bull is the chief source of contagion, the 
treatment should start with him. Veterinarians recom- 
mend that the sheath and external genitals of the bull 

1 Law, "Diseases of Cattle," U. S. Department of Agriculture, 
1908. 

2 MacFadyean, Journal of the Royal Agricultural Society^ 
1909, p. 337. 

^ Law, loc. ciL, p. 166. 



STERILITY 125 

be thoroughly disinfected with a sohition of bichloride 
of mercury 1 to 2000 containing one per cent of copper 
sulfate. The same disinfectant should be used to flush 
the vagina of the suspected cows. Nocard ^ recommends 
the following solution for cleansing the external genitals, 
anus and tail of the aborting cow : 

Distilled or pure rain water .... 2 gallons 

Hydrochloric acid 2\ ounces 

Corrosive sublimate 2\ drachms 

These ingredients should be thoroughly mixed. 

In Denmark, according to Dalrymple,^ all membranes 
and the foetus are buried in lime and the internal genital 
organs of the cow are thoroughly disinfected with a one 
per cent solution of creolin or a half per cent solution of 
lysol. The external genitals of the bull and of cows about 
to be bred are treated with the same solution. 

All aborted tissues must be burned and the premises 
thoroughly disinfected. This treatment is uncertain 
and often unsuccessful. A breeder will generally gain 
time in the eradication of abortion from his herd by insist- 
ing upon never using a contaminated male on young heifers 
bred for the first time or upon cows known to be free from 
the disease. All infected and aborting cow^s should be 
separated absolutely from the females w^hich have never 
aborted. All cows known to be free from the disease 
should be covered by a bull also known to be free from 
infection. The uninfected herd must be guarded from 
infection from the diseased herd. This plan will even- 
tually build up a clean herd and no other method so far 
devised is certain to accomplish this desirable result. 

^ Dalrymple, "Veterinary Obstetrics," p. 59. 
2 Loc. cit. 



126 THE BREEDING OF ANIMALS 

The problem, of treating the bull and cows known to 
be infected is quite distinct from the building up of a 
clean herd. Fortunately this infection is not transmitted 
by heredity and is not necessarily spread from mother 
to offspring by direct infection. It is, therefore, possible 
for a breeder to retain in the young animals from the 
infected herd the best products of his skill and experi- 
ence. When a cow from the infected herd aborts, all 
tissues expelled from the uterus should be promptly 
burned and the stall thoroughly disinfected by a generous 
use of lime. The vagina of the cow should be disinfected 
with the solution described on p. 125. The aborting 
cow should be permitted to rest at least six months before 
breeding again. The prevention of abortion in a cow 
already pregnant has been successfully accomplished in a 
number of instances by internal applications of carbolic 
acid. Taylor's^ successful experiments in preventing 
impending abortion are worthy of note. A description 
of the treatment of one cow is typical and will serve as 
an example of the methods which w^ere generally successful. 
A grade cow four years old that had aborted the previous 
year and was known to be infected with granular vaginitis 
was given the following treatment : At the beginning 
of the fourth month of the period of gestation she was 
given 200 cubic centimeters of a four per cent solution 
of carbolic acid in her feed. The dose was increased to 
250 cubic centimeters the fifth month and to 300, 350 and 
400 cubic centimeters for the sixth, seventh and eighth 
months respectively. This cow dropped a strong healthy 
calf at the end of the normal period of gestation. A sum- 
mary of the results in one herd treated by Taylor shows 

^ Taylor, Montana Experiment Station, Bulletin No. 90, 
1912. 



STERILITY 127 

that in 1908 there were fifteen per cent abortions, in 1909 
twenty-five per cent, in 1910 five per cent, and in 1911 
two-and-one-half per cent of abortions. The carboHc 
treatment was begun in December, 1909. It is recom- 
mended that infected males be treated in the same manner.^ 

120. Diagnosis of contagious abortion. — This disease 
is so widespread and causes such serious consequences 
when once well established in a herd that it is often of 
the greatest importance to be able to detect its presence 
in animals, even those which are not at the time pregnant. 
Various attempts have been made with greater or less 
success to secure a reliable diagnostic agent which would 
make it possible for the breeder to know which animals 
in his herd are infected with the germ of contagious abor- 
tion and thus be able to separate the infected individuals 
from those which are healthy. 

The first substance of this character to be used was 
similar to tuberculin and mallein. The name of '' abor- 
tin " was given to this substance by MacFadyean and 
Stockman. This material was to be injected into the 
circulation of the cows of a herd. The infected cows 
showed a considerable rise in temperature following the 
infection. The healthy cows showed but little or no 
increase in temperature. BrtilP at Vienna, after testing 
this method on a large number of cows, concluded that 
abortin was an unreliable diagnostic agent for determining 
the presence of contagious abortion in cattle. Other 
investigators have reported similar unfavorable results 
from the use of this material. 

^ See also Good, Kentucky Experiment Station, Bui. No. 165 ; 
Surface, Kentucky Experiment Station, Bui. No. 166 ; MacNeal 
and H. W. Mumford, Illinois Experiment Station, Bui. No. 152. 

^Bnill, "Berl. Tierartzt Woch.," Bd. 27, pp. 721-727. 



128 THE BREEDING OF ANIMALS 

In cases of typhoid fever, the so-called agglutination 
test was found to be a fairly reliable agent for the diagnosis 
of this disease. In 1907-8, Ginstead in Denmark applied 
this test successfully to cows suffering from contagious 
abortion. Later MacFadyean and Stockman ^ published 
the results of a limited number of investigations, report- 
ing unfavorably upon this method. Later Holth and 
Wall,^ after an extensive series of investigations involving 
hundreds of cows, concluded that the agglutination test 
was a reliable diagnostic agent but probably subject to 
larger error than the complement fixation test. 

121. The complement fixation test.^ — Neither the 
abortin nor the agglutination test has proven entirely 
satisfactory under all circumstances. The most reliable 
test now available is the complement fixation test.^ 
Connaway of the Missouri Experiment Station says, 
" This test has been found very reliable as a diagnostic 
method in contagious abortion. The result of the test 
on some infected herds shows that in old infected herds 
the per cent of re-acting animals runs from 60 to 90 per 
cent." This is a highly complicated and difficult test 
to make, but will with practical certainty cause a reaction 
in cows that have been infected. Cows that have aborted 
may develop an immunity to this disease, and when this 
has occurred the complement fixation test cannot be 
used to distinguish between those cows which will abort 

1 MacFadyean and Stockman, "Report of the Departmental 
Committee to inquire into Epizootic Abortion," Pt. I, and 
Appendix, London, 1909. 

2 "Berl. Tierartzt Woch.," Bd., pp. 686-688, 1909. 

^See Surface, Kentucky Exp. Sta. Bui. No. 166; MacNeal 
and Mumfoi^d, Illinois Exp. Sta. Bui. No. 152 ; Russell, Science, 
N. S., vol. 34, p. 494, 1911; Wisconsin Research, Bui. No. 24, 
1912. 

^ Missouri Experiment Station, Bui. 131, p. 486. 



STERILITY 129 

and those which are immune. The great value of this 
lies in the fact that the aborting cows may be entirely 
separated from the healthy members and eventually 
by this separation the disease may be entirely eliminated 
from the herd. 

122. Sterility of free-martins. — The birth of twins 
among cattle is frequent. When a cow gives birth to 
twins, one a female and the other a male, the female is 
called a free-martin and is generally sterile. So far as 
known, this condition does not exist among any other 
known species of animal. Among sheep, for example, 
where twins are very common, the female twin born with 
a male may be even more fertile than the single born 
lamb. No case of sterility among human twins has ever 
been recorded where the sterile condition w^as believed 
to be due to the fact that one twin was a male and the 
other a female. Among cattle where both twins are of 
the same sex both are fully fertile. This is, therefore, 
a remarkable biological fact which it is difficult to explain. 
Morse ^ reports that Dr. Luer found 113 cases of twins, 
one a male and the other a female, in the records of the 
East Prussian Holland Herd Book. Of this number all 
the females were sterile except six. 

The author has examined a considerable number of 
free-martins and in every case of sterility the female 
reproductive organs have been imperfectly developed. 
One case examined is typical. A grade Aberdeen Angus 
had every external appearance of a female. The loca- 
tion and form of the external genital organs was that of 
a true female. There were only two peculiarities which 
were visible externally. A tuft of long hair resembling 
the growth on the sheath of the bull grew from the lower 

1 Morse, Breeder's Gazette, vol. 64, p. 346. 

K 



130 THE BREEDING OF ANIMALS 

extremity of the vulva. The mammary glands were 
very small and but little developed and resembled more 
the rudimentary mammary glands of a bull than the 
normal glands of a cow. At two years of age this sup- 
posed cow had never come in heat. She was permitted 
to run in the same paddock with two mature bulls for a 
period of six months, but never came in heat. This 
animal was slaughtered and the reproductive organs 
removed for examination. It was found that the animal 
had a vulva and a very short vagina-like organ ending 
in a blind sac. No uterus, Fallopian tubes or ovaries 
were found. There was also found a rudimentary penis. 
It seems probable that sterile free-martins are imperfect 
males or hermaphrodites. It is not possible at this time 
to give any satisfactory explanation of why there should 
exist a greater tendency to hermaphroditism when twins 
of different sex are born than twins of identical sex. It 
is still more difficult to explain why this phenomenon 
should occur exclusively among cattle. It is possible 
that the explanation o£ this phenomenon is associated in 
some way with the production of identical twins, but 
this does not offer any satisfactory explanation of why 
this strange occurrence should be found in the bovine 
species alone. 



CHAPTER VII 
HEREDITY 

The characteristics of the individual are determined 
by heredity and development. What an animal may 
become, depends on the heritage received from its 
ancestors. No organic being can be developed beyond 
the limits imposed upon it by its inheritance. A favor- 
able environment and good training will permit the 
individual to achieve the full limit of its possibilities, 
but no amount of training and no combination of favor- 
able circumstances can ever lift the individual above the 
inheritance which it has gained through its parents. 
The trotting horse may have inherited the capacity to 
trot a mile in two minutes, but if its development has 
been arrested by insufficient food and an unfavorable 
climate, and no attempt has been made to develop its 
inherent ability to go fast, it can never achieve the full 
measure of its possibilities. It is also true that if a horse 
has not inherited from a line of trotting ancestors the 
ability to go fast at the trot, no amount of training and 
no system of feeding can develop the animal to a point 
where it will be able to trot a mile in two minutes. 

Heredity then represents what an animal really is or 
can become. The individual cannot in any manner or 
to any extent influence its own heredity. An animal's 
inheritance is determined by its ancestors. The indi- 

131 



132 THE BREEDING OF ANIMALS 

vidual may profoundly Influence its development through 
seeking a favorable environment and through habitual 
use or disuse of its inherited tendencies. 

123. Development. — The full realization of the in- 
herited capacities of an animal is accomplished through 
its environment and training. The most important 
factors concerned in the environment of an animal are 
food and climate, and these acting upon the inherited 
qualities of the animal may profoundly influence the 
actual characteristics of the individual. In order that 
the inherent characteristics of any organic being may 
attain to full development, a sufficient supply of food 
must be available. When food is scarce, the individual 
may be unable to develop, and what it may ultimately 
become, may be greatly influenced by this lack of 
food. A full and sufficient food supply may cause the 
individual to develop beyond the average condition of 
the species, particularly if the average environment does 
not furnish a generous supply of food. 

The training of the individual, likewise, is an important 
factor in determining its ultimate development. Any 
function of an animal which is not exercised may retro- 
grade or in some cases practically disappear. The 
milking function in domestic cattle is a good example of 
the influence of both development and exercise or train- 
ing. The highly developed dairy breeds of cattle, when 
generously fed and carefully milked, produce very much 
more milk than their wild ancestors. Individual cows 
of modern dairy breeds, if starved and carelessly milked 
or neglected, will fail to develop the highly specialized 
milking function. 

124. Heredity defined. — In much of the literature 
of biology pertaining to heredity, there is a lack of definite- 



HEREDITY 133 

ness in the use of terms. The Kterature of animal-breed- 
ing is still less exact in its terminology. It seems impor- 
tant, therefore, that in the very beginning we should have 
as clear a conception as possible of the definitions of 
heredity which have been proposed. Heredity is the 
organic relation existing between an individual and its 
ancestors. It is the continuous biological thread connect- 
ing generations of organic beings. Heredity is '' organic 
resemblance based on descent." ^ Thomson ^ has defined 
heredity as " the organic or genetic relation between 
successive generations." " Understood in its entirety," 
says Herbert Spencer,^ " the law is that each plant or 
animal, if it reproduces, gives origin to others like itself; 
the likeness consisting, not so much in the repetition of 
individual traits as in the assumption of the same general 
structure." '' The transference of similar characters 
from one generation of organisms to another, a process 
effected by means of the germ-cells or gametes." ^ '' By 
inheritance," says Lock,^ '' we mean those methods and 
processes by which the constitution and characteristics 
of an animal or plant are handed on to its offspring, this 
transmission of characters being, of course, associated 
with the fact that the offspring is developed by the pro- 
cesses of growth out of a small fragment detached from 
the parent organism." Another definition of heredity 
is that it is the tendency of the offspring to be like the 
parents. There exists a definite organic resemblance or 

^ Castle, " Heredity in Relation to Evolution and Animal 
Breeding." 

2 Thomson, "Heredity" (1908), p. 13. 

^Herbert Spencer, " Principles of Biology," vol. I, p. 301. 

"* R. H. Lock, " Recent Progress in the Study of Variation, 
Heredity and Evolution," 1906, p. 292. 

^ Loc. ciL, p. 1. 



134 THE BREEDING OF ANIMALS 

relation between parents and offspring. This relation is 
a universal biological phenomenon and is called heredity. 
There exists a continuous line of descent from generation 
to generation. The mechanism of heredity is to be found 
in the protoplasm of the germ-cells. The stream of 
descent is from germ-cell to germ-cell. The soma- or 
body-cells constitute in a sense only a temporary abiding 
place for the germ-plasm. 

125. Heredity and variation not antagonistic. — It is 
not stating the facts correctly to maintain that the tend- 
ency of offspring to be like the parent, which we call 
heredity, is opposed by the universal tendency of organ- 
isms to vary. These are but two phases of the same 
phenomenon. " Living beings do not exhibit unity 
and diversity," says Brooks, "but unity in diversity. 
These are not two facts but one. The fact is the indi- 
viduality in kinship of living beings. Inheritance and 
variation are not two things but two imperfect views 
of a single process." There is a sense, of course, in which 
variation is opposed to heredity. It is conceivable that 
recombinations of characters may occur in the germinal 
substance, and these new combinations may cause such 
modification of characters already present that the new 
organism may be radically changed. 

Heredity is the genetic relation of parents and offspring. 
On the average the offspring will be like the parents. 
But this relation admits of variations within more or less 
definitely prescribed limits. The offspring have an 
individuality all their own, but this does not preclude the 
existence of a genetic continuity which is the common 
heritage of parents and offspring. 

126. The kinds of heredity. — Every individual is 
the result of a union of the germ-plasm of two individuals. 



HEREDITY 135 

The evidences of this dual origin are not always exhibited 
in the same manner. In some individual offspring the 
characters of one parent may predominate, in others 
the parental characters seem to blend so successfully 
that often the child differs from either parent, while in 
still others the characters of both parents appear in the 
offspring with apparently equal force but, instead of blend- 
ing, the characteristics of the parents appear clearly as 
distinct and easily recognizable qualities. These methods 
of transmission wxre called by Galton, blending, alternate 
and particulate inheritance. 

127. Blending inheritance. — In this type of inherit- 
ance the characters of the offspring represent a blending 
or intermingling of the characters of the two parents. 
Stature in man may and often does represent the blend- 
ing of the statures of the two parents. The stature of 
the son or daughter is taller than the shorter parent, but 
falls short of that of the taller parent. When a rela- 
tively small mare is mated with a heavy draft stallion, 
the resulting offspring is never so large as the sire nor so 
small as the dam, but represents an approach to a mean 
between the two. Another example of blended in- 
heritance is to be observed in the cross-bred lambs 
resulting from the union of a sire of the coarse wool type 
and a dam belonging to the fine wool or Merino breed. 
The lambs of such a cross are covered with wool which in 
respect to density, length of staple and fineness of fiber 
represents a blending of the characters of the parents. 

In some cases of supposed blending inheritance, the 
characters have been observed to follow the law of domi- 
nance and segregation discovered by Mendel. 

128. Alternative inheritance. — A charact«er may be 
transmitted intact from one parent directly to the off- 



136 . THE BREEDING OF ANIMALS 

spring without apparent modification by the other parent. 
In this type of inheritance one parent seems to possess a 
predominating influence in determining the characteristics 
of the offspring. Many examples of this type of heredity 
are to be observed among the domestic animals. The 
white face of the Hereford breed of cattle is invariably 
transmitted, even when one parent belongs to a widely 
different breed. The quality of speed in horses is un- 
doubtedly transmitted, sometimes in accordance with 
Galton's alternative inheritance. Fecundity in the do- 
mestic fowl has been shown by Pearl to be transmitted 
through the male. The hen inherits fecundity directly 
from the sire. The ability to lay a large number of eggs 
is not transmitted from the mother to the immediate 
female offspring, but to her male offspring. 

" Hence if the daughters of high producing hens are 
selected, one does not get in them the high productiveness 
of the mother. It is her sons that inherit the character, 
although they cannot show it except in their offspring." ^ 

129. Particulate or mosaic inheritance. — The char- 
acters of the parents are often transmitted in such a 
manner that they are not in any sense blended but appear 
rather as a mosaic. The color character is frequently 
inherited as a mosaic. A very good example of this 
kind of inheritance is seen in the Holstein Friesian breed 
of cattle. This breed is black and white, these colors 
appearing in definite, clearly defined areas and not blend- 
ing. The Holstein Friesian breed was originated by 
crossing a black breed and a white breed of cattle. The 
colors black and white in other animals seem to behave 
in a similar manner. When white hogs are mated with 
black, the -offspring are always spotted. Recently it 

1 Morgan, "Heredity and Sex," p. 213. 



HEREDITY 137 

has been suggested that particulate inheritance is in 
reahty true alternative inheritance in which the mosaic 
result is caused by the absence of the factor for uniform- 

130. Mendelian inheritance. — Progress in the investi- 
gation of breeding problems has come through statistical 
investigations, by cytological studies of the germ-cells 
themselves, and by experimental breeding. Each of 
these methods has contributed evidence of value in the 
direction of a more definite understanding of the prin- 
ciples of heredity. In recent years experimental breeding 
has contributed very materially to our knowledge of 
the science of heredity. Improvements in the technique 
of cell studies has supplemented the results obtained by 
experimental breeding. It is a significant fact that the 
hypotheses based upon experimental breeding agree in 
many important particulars with those derived from 
minute investigations of the origin and development of 
the germ-cells. 

Perhaps the most remarkable series of investigations 
in experimental breeding were those carried on by Johann 
Gregor Mendel, an Austrian monk. These interesting 
investigations gave a new impetus to the study of theoreti- 
cal heredity and particularly to the practical improve- 
ment of plants and animals. The investigations of Mendel 
were first published in 1865 and over twenty years later 
were again published in the Transactions of the Natural 
History Society of Briinn. No attention was given to this 
important contribution to the science of breeding, and 
even Nageli, a former teacher of Mendel, to whom the 
results were submitted, failed to recognize their funda- 
mental significance. It was not until the year 1900 

1 Walter, "Genetics," p. 164. 



138 THE BREEDING OF ANIMALS 

that three great investigators, De Vries in Holland, Von 
Tschermak in Austria, and Correns in Germany, simul- 
taneously discovered the published results of Mendel and 
recognized their great fundamental importance. 

131. The experiments of Mendel. — Mendel selected 
for his experiments the common garden pea. It is not 
certain that he fully recognized the wisdom of making 
such selections as were finally made for his work, but at 
any rate he selected two varieties of peas differing in a 
simple character but each firmly fixed in the parent 
variety. The peas were also self-fertilizing, and accidental 
mixture by cross fertilization was thus avoided. The 
characters selected by Mendel were " purple or white 
flowers," " yellow or green cotyledons," and " round or 
wrinkled seeds." He found that all of these characters 
were firmly fixed and bred true. These varieties were 
crossed and the progeny were bred pure for many suc- 
ceeding generations. 

He decided upon the simple character of color and 
selected a green seeded and yellow seeded variety. Recip- 
rocal crosses were made, and from each cross the result- 
ing peas were all yellow. Because the yellow color in 
the cross appeared in every case, he called it the dominant 
character; and the green color which did not appear in 
the first generation was called a recessive character. 

All the yellow seeds of the first generation resulting 
from the original cross were planted. In the second 
generation Mendel discovered that both green and yellow 
seeds appeared. In calculating the relative proportion 
of the two colors, he found that about one-fourth of the 
seeds were green and the remaining three-fourths yellow. 
The green seeds and yellow seeds were planted separately 
and it was found that the green seeds produced only 



HEREDITY 139 

green seeds. They were planted for several generations 
and always came true, showing no yellow character. 
When the yellow seeds were planted, however, Mendel 
found that a certain proportion of the yellow seeds had 
both green and yellow offspring and a certain proportion 
had only yellow offspring. The latter remained fixed 
and true in character when bred for several generations. 
The results of these investigations carried through 
many generations indicated that there was a certain 
mathematical ratio traceable in the offspring resulting 
from the crossing of these two distinct varieties of peas. 
In these results Mendel found that in the first genera- 
tion the dominant character (yellow seed) appeared to 
the exclusion of the green color. In the second genera- 
tion he found that 25 per cent of the offspring were green 
and 75 per cent apparently yellow. If the green peas 
were planted, they produced only green peas, but when 
the yellow peas were planted, they produced 25 per cent 
pure yellow, 50 per cent mixed or hybrid (yellow and 
green), and 25 per cent pure green. The pure yellows 
and pure greens continued to breed true, but the 50 per 
cent '' hybrid " peas continued to split up in each genera- 
tion in the proportions of 25 per cent pure green, 25 per 
cent pure yellow, and 50 per cent hybrid. 

132. The law of dominance. — From these results 
Mendel formulated the law of dominance, which is that 
when two contrasting characters are bred together the 
offspring in the first (Fi) generation will all exhibit the 
dominant character. 

133. The law of segregation. — When the individuals 
comprising the first generation are interbred, the resulting 
offspring (F2 generation) will possess the characters in 
the proportion of three of the dominant character to one 



140 



THE BREEDING OF ANIMALS 



of the recessive. The recessive character is pure and will 
breed true. The individuals possessing the dominant 
character will be made up of one-third pure dominants 
and two-thirds hybrid dominants in which the recessive 



Dornimnt 



Recessive 



Y(yeJIoW) 




dc green) 



Y(Q.) ihyhrjd yeJhwy 



(pureyeJlow)Yy ^VtGj QG Cjoure ^een) 



ix icm GG 




I)^) 2g[ 




Fig. 16. 



Diagram illustrating mendelian inheritance of yellow and 
green characters in the garden pea. 



character will reappear in the next generation. This may 
be more clearly shown in the preceding diagram (Fig. 16). 
Mendel's hypothesis affirms that when animals or 
plants of contrasted characters are bred together, these 
characters do not blend in the germ-cells of the offspring. 



HEREDITY 141 

Fifty per cent of the germ-cells will contain the dominant 
character and fifty per cent the recessive character. This 
is true of both male and female germ-cells. 

134. Unit characters. — Mendel's theory presupposes 
the existence of unit characters, so-called because they 
are transmitted as independent units. There exist in 
every organic being a very large number of unit char- 
acters, and these may be determined by experimental 
breeding. Up to the present time a relatively small 
number of unit characters have been definitely differ- 
entiated and described, but our knowledge in this direc- 
tion is being rapidly extended. 

135. Gametic purity. — In one stage of maturation 
of the male and female germ-cells, the nucleus of each 
contains but half the normal number of chromosomes 
characteristic of the species. This is the final stage in 
the maturation process before fertilization takes place. 
The germ-cells in this stage are called gametes. The 
fertilized egg-cell which results from the union of a ma- 
ture sperm and egg-cell (gametes) is called a zygote 
(fertilized egg-cell). The zygote, therefore, contains the 
normal number of chromosomes characteristic of the 
species, one-half derived from the Qgg and one-half from 
the sperm-cell. Gametic purity is a term used to desig- 
nate the discontinuous nature of unit characters. The 
gamete in Mendel's pea contains the factor necessary for 
the production of yellow seeds, or it does not.^ 

The terms homozygous and heterozygous were pro- 
posed by Bateson to designate the fundamental consti- 
tution of the germ-cells in respect to inherited characters. 
" An individual is said to be homozygous for a given 

1 Darbishire, ** Breeding and the Mendelian Discovery," 
p. 217. 



142 THE BREEDING OF ANIMALS 

character when it has been formed by two gametes each 
bearing the character, and all the gametes of a homozygote 
bear the character in respect of which it is homozygous. 
When, however, the zygote is formed by two gametes of 
which one bears the given character while the other does 
not, it is said to be heterozygous for the character in 
question, and only half the gametes produced by such a 
heterozygote bear the character. An individual may be 
homozygous for one or more characters, and at the same 
time may be heterozygous for others." ^ 

The conception of " gametic purity " as originally 
stated requires some modification. It is no longer held 
that characters are transmitted as units, but rather the 
factors which combine to form characters. The factors 
are so far purely imaginary. 

When mendelism was first seriously considered, there 
was no doubt among its most enthusiastic exponents 
that the characters existed in a pure unmixed state in 
the gamete.^ 

136. Application of Mendel's law. — Can the practical 
breeder apply the principles of heredity embodied in 
Mendel's law to the improvement of the domestic ani- 
mals ? The domestic animals are valued by man because 
of certain desirable characteristics which they possess. 
These characteristics are clearly recognized by the breeder. 
The meat animal is produced because it is endowed with 
certain qualities which give it a special value either to 
the consumer or the producer. The dairy cow is highly 
prized because she has the ability of producing large 
quantities of milk, cream or cheese. The horse is the 
burden-bearer. Its value depends on the amount 

iPunnett, "Mendelism," 1913, p. 28. 

^See Castle, " General Heredity," vol. V, No. 3, p. 93. 



HEREDITY 143 

of energy it can develop either in tractive power for pull- 
ing heavy loads or in the form of speed or graceful action 
for the pleasure of the owner. Other animals are main- 
tained in a state of domestication for other values of 
various kinds which contribute to the food, clothing or 
pleasure of man. In a sense the producer of live-stock 
may be compared to a manufacturer who employs capital, 
labor, raw^ materials and efficient machines for the pro- 
duction of more desirable and concentrated products. 
In this comparison the raw materials are the grain, hay 
and grass ; and the efficient machine is the animal. The 
farmer's success and the interests of the consumer as 
well are greatly dependent upon the efficiency of this 
animal machine. Can Mendel's law be utilized in the 
efforts of the breeder to increase the efficiency of animals ? 
If so, what does the breeder need to know in order to 
utilize the law of Mendel in further enhancing the value 
of the prevailing types of domestic animals ? 

137. The complexity of animal characters. — It must 
be recognized in the beginning that the qualities which 
are commonly mentioned by the breeder as highly desir- 
able are generally the result of a combination of many 
characters. These combinations do not behave as simple 
unit characters. One of the first steps in the application 
of Mendel's hypothesis to practical breeding must be to 
analyze the valuable qualities of animals and determine 
as far as possible the unit characters. It is probably 
true that some combinations will behave in transmission 
in the same manner as simple unit characters. But if 
there are complex characters which behave in this manner 
they must be determined by careful investigation. When 
the qualities of an animal have been differentiated and 
their behavior in transmission determined, then the prac- 



144 THE BREEDING OF ANIMALS 

tical breeder may base his breeding methods upon the 
principles of segregation and dominance which are founda- 
tion stones in the theory of mendehan inheritance. 
• It will also be important to remember that to utilize 
the mendelian principle in the breeding of animals, the 
breeder must be dealing with contrasting characters. 
In the larger number of cases, the useful qualities of the 
highly improved animals of the farm are but modifica- 
tions of characters which were already present in the 
wild forms. The function of milk secretion is common 
to all mammals. The domestic cow is valuable because 
this function has, through selection and skillful mating, 
been gradually improved. The quality of giving a small 
quantity of milk found in the wild cow, and the quality 
of giving a large quantity of milk as present in the highly 
improved dairy cow, are not contrasting characters. 
The one is but a modification of the other and is probably 
the result of accumulated fluctuating variations which 
have been preserved by methodical selection. It will be 
interesting to note here some characters among animals 
which have already been found to conform to Mendel's 
law. 

138. The inheritance of polled and horned character 
in cattle. — Examples of Mendel's law are much more 
frequent among plants than animals. The complicated 
nature of animal characteristics has made it difficult to 
trace the workings of Mendel's law so far as it is related 
to many animal characters. It is also more difficult 
to find contrasting characters. An exception to the 
above must be noted in the case of the horned and polled 
characters in cattle. Whenever a pure polled animal 
is mated with a pure horned animal, the offspring in the 
first generation are all polled. If the first generation 



HEREDITY 



145 



offspring are interbred, the polled and horned characters 
separate in the second generation in the proportion of 
25 per cent pure polled, 50 per cent hybrid polled, and 
25 per cent pure horned. The pure polled individuals, 



Po//e</ 



Homed 




PiHY 



PP' z W PP' 



PP zPlH) HH 



PP PP PP zP(H) 




1- Polled Ny6r,d 

2- Pure Polled 

3- Pure Homed 

Fig. 17. — Diagram illustrating mendelian inheritance as exhibited 
in the transmission of polled and horned characters in domestic cattle. 



if bred to others of their own kind, produce only pure 
polled offspring. If the pure horned offspring likewise 
are mated with pure horned individuals, their offspring 
produce pure horned offspring. If the 50 per cent hybrid 
polled individuals are bred to other hybrid animals, the 



146 THE BREEDING OF ANIMALS 

result is the same as in the second generation. The off- 
spring will be 25 per cent pure polled, 25 per cent pure 
horned, and 50 per cent hybrid polled. (See Fig. 17.) 

This principle has been repeatedly used in the produc- 
tion of polled breeds of cattle. The only practical diffi- 
culty is encountered in determining which of the second 
generation are pure polled and which are hybrid polled. 
This difficulty can be overcome only by repeated matings 
and by observation of the offspring. 

139. Theory of pure lines. — The practical breeder 
of animals has depended almost entirely upon methodical 
selection for the improvement of domestic animals. It 
was Darwin's opinion that the improvement accom- 
plished in the desirable qualities of animals and plants 
was due to the persistent selection of desirable continuous 
variations. In bringing about improvement, therefore, 
the breeder only required keen powers of observation 
to detect any variations in a standard sort which were 
better than the qualities of the ancestors. By selecting 
these varieties and continuing this process for many gen- 
erations, highly improved sorts were ultimately developed 
which came true when bred together. 

In the practical application of this theory, it has been 
frequently discovered that the limits of improvement 
through selection were quickly reached. Apparently 
the degree of improvement could not be carried beyond 
a certain definite point. In a more careful analysis of 
the fundamental basis of improvement by selection, 
Johanssen ^ has demonstrated that very many of the 
domestic plants are not possessed of single characters 
only, but are a mixture. The selection exercised* by 
man in such cases is essentially a process of selecting out 

1 Johanssen, 1909, "Elemente der exakten Erblichkeitslehre." 



HEREDITY 147 

the most desirable strain and gradually eliminating the 
less desirable. This is the pure line theory and is now 
generally accepted as applying to many cases of improve- 
ment, especially among plants. 

An acceptance of this theory recognizes the fact that 
no amount of selection can improve a pure line after it 
has been separated by continuous selection. 

An hypothetical example of pure line selection among 
animals might be imagined in the case of the wool of sheep. 
The wool produced under a given set of environmental 
conditions in a flock of sheep might vary from eight to 
twelve pounds. In the germ-cells of a given individual, 
we may assume that determiners are present for the pro- 
duction of eight, ten and twelve pounds. In breeding, 
these varying tendencies may be separated. It is con- 
ceivable that some of the offspring may have inherited 
the tendency to produce twelve pounds of wool, while 
others may have inherited the tendency to produce eight 
pounds. Through many generations of intelligent selec- 
tion, the flock-master may bring about a more or less 
complete separation of the tendency to produce twelve 
pounds of wool and may thus increase the average pro- 
duction of wool from his flock. The application of this 
theory to animal-breeding is more difficult than to self- 
fertilizing plants, but the difficulties are partially removed 
by close interbreeding. 

140. Hallett's wheat-breeding. — The pure line method 
of breeding probably explains Hallett's unusual success 
in the improvement of wheat in Great Britain. However, 
it must be said that Hallett believed that improvement 
within a pure line of selection was possible. Hallett's 
method may be best described by using his own words : 

" A grain produces a ^ stool ' consisting of many ears. 



148 THE BREEDING OF ANIMALS 

I plant the grains from these ears in such a manner that 
each ear occupies a row by itself. ... At harvest, 
after the most careful study and comparison of the stools 
from all these grains, I select the finest one, which I 
accept as proof that its parent grain was the best of all, 
under the peculiar circumstances of that season. This 
process is repeated annually, starting each year with 
the proved best grain, although the verification of this 
superiority is not obtained until the following harvest. 

" During these investigations no single circumstance 
has struck me as more forcibly illustrating the necessity 
of repeated selection than the fact, that of the grains in 
the same ear one is found greatly to excel the others in 
vital power." ^ 

Hallett's experience has demonstrated, first, that 
great improvement may be secured by this method of 
selection. Second, he advocated the " ear to row " 
method. Third, it is probable that the results may be 
satisfactorily explained by Johanssen's pure line theory. 

141. The presence and absence hypothesis. — In 
Mendel's conception of the theory of dominant and reces- 
sive characters, there existed a definite determiner for 
both the dominant and recessive characters. Each char- 
acter appeared in the gametes in a definite form. Later 
investigations have pointed to the fact that the dominant 
character may be due to the presence of a specific deter- 
miner, while the recessive character may be due to its 
absence. This conception of the behavior of the mende- 
lian pair of characters is quite different from MendeFs 
explanation. 

The presence and absence theory has contributed 
materially to the science of genetics. This hypothesis 

^ Journal of the Royal Agricultural Society, vol. 22, p. 371. 



HEREDITY 149 

has made it possible to harmonize many of the observed 
phenomena with the mendeUan principle. It has also 
directed the attention of investigators to the fundamental 
nature of the characters themselves. Great progress 
will undoubtedly be made in the future in the direction 
of a more thorough study and consequently better under- 
standing of the real nature of the characters of both plants 
and animals. 

In the investigations on the eye color of man, it has 
been found that the dominant character is due to a brown 
pigment, while the recessive character is the result of the 
absence of this pigment. Darbishire ^ has clearly indi- 
cated the application of this theory in the case of the 
round pea and the wrinkled pea. The quality of round- 
ness or wrinkledness as found in the garden pea is due 
to a difference in the amount of starch in the pea. In 
the case of the wrinkled pea, all of the sugar content is 
converted into starch. In the round pea a much more 
complete transfer of sugar to starch is accomplished. 
The inference is that in the round pea there is present 
something in the germ-cell that so affects the physiological 
processes in the cell that the sugar is more or less com- 
pletely turned to starch. The something which deter- 
mines this change of sugar to starch in the round pea is 
absent from the germ-cell in the wrinkled pea. There- 
fore, we have two varieties of pea that are clearly different. 
When the wrinkled pea and the round pea are crossed, 
they behave in accordance with the mendelian law. It 
is not necessary in this case to assume that the determiner 
which ultimately results in a round pea is entirely absent 
in the wrinkled pea, but it seems to be entirely correct 

1 Darbishire, "Breeding and the Mendelian Discovery," p. 
127. 



150 THE BREEDING OF ANIMALS 

to assume that there exists an insufficient quantity of 
this substance and hence an incomplete transposition of 
sugar to starch in the wrinkled pea. 

It is not at present possible to apply the presence and 
absence hypothesis to all cases of apparent mendelian 
inheritance. That it applies to a very large number of 
characters is obvious, but as pointed out by Darbishire 
there are many cases which cannot at the present time 
be explained on this theory, and in fact will be obstacles 
in the way of its general application. Some characters 
seem to be dominant in one class of plants or animals 
and recessive in another. The polled character in cattle 
is unquestionably dominant, while the possession of horns 
is a recessive. In the case of sheep the reverse seems to 
be true. The white color of pigs is dominant to black, 
but the black color of sheep is dominant to white.^ 

142. The theory of mutations. — It is clear that all 
improvements in the domestic animals must come through 
variation. If the offspring was always an exact repro- 
duction of the parent, improvement would be impossible. 
But how have the improved qualities now possessed by 
our domestic animals come about? Have these qualities 
come through a gradual and continuous .series of changes, 
each better than the last, or have they come through 
sudden and radical variations ? A study of the ancestral 
history of both plants and animals gives clear evidence 
that new types have originated by both kinds of variation. 

143. Two important classes of variation. — Darwin 
recognized these two distinct types of variation, but 
believed that the most important changes in organic 
beings were due to small but gradual and continuous 
variations in a given direction. In his earlier writings 

1 Punnett, "Mendelism," p. 29. 



i 



HEREDITY 151 

Darwin emphasized the great importance of continuous 
or fluctuating variations. He says, '' It may be doubted 
whether sudden and considerable deviations of structure 
such as we occasionally see in our domestic productions, 
more especially with plants, are ever permanently prop- 
agated in a state of nature. Almost every part of every 
organic being is so beautifully related to its complex 
conditions of life that it seems as improbable that any 
part should have been suddenly produced perfect, as 
that a complex machine should have been invented by 
man in a perfect state." 

Sudden variations were called by Darwin discontinuous. 
Variations frequently occur which vary widely from 
the parent form. Examples of this kind of variation 
are common in both plants and animals. The normal 
fruit of a peach tree is a typical peach having a rough 
skin and a flavor and color peculiar to the peach. 
Branches of peach trees, however, sometimes produce a 
fruit known as a nectarine. This is smooth, smaller 
than the peach, and possessed of a color, flavor and physical 
consistence markedly different from the normal fruit of 
the peach. 

Among animals mutations frequently occur. Varia- 
tions in the number of digits have been recorded by a 
large number of investigators. Huxley describes the 
case of a man born with six fingers on each hand and six 
toes on each foot. Four children were born to this man. 
The first, a male child, was born with six fingers on each 
hand and six toes on each foot. The second child, a 
boy, had five fingers and five toes, but one toe was de- 
formed. The third child, also a boy, had five perfect 
fingers and toes, but the fourth child, a girl, although 
having the normal number of digits, had deformed thumbs. 



152 THE BREEDING OF ANIMALS 

The mutation appearing in the father was not only a 
radical variation, but there existed a strong tendency to 
transmit the abnormality. The strength with which 
mutations are transmitted is still further indicated by 
the later history of the sons and daughters of the father. 
" Salvator had four children — they were two boys, a 
girl, and another boy — the first two boys and the girl 
were six-fingered and six-toed like their grandfather; 
the fourth boy had only five fingers and toes. 

" George had only four children ; there were two girls 
with six fingers and six toes ; there was one girl with six 
fingers and five toes on the right side, and five fingers -and 
five toes on the left side, so that she was half-and-half. 
The third, Andre, you will . recollect, was perfectly well 
formed, and he had many children whose hands and feet 
were all regularly developed. 

" Marie, the last, who of course married a man who 
had only five fingers, had four children : the first, a boy, 
was born with six toes, but the other three were normal." ^ 

Some marked variations among the domestic animals 
which have been recorded from time to time and which 
are probably true mutations may be mentioned. The 
normal foot of domestic swine is cleft, but solid-hoofed 
hogs are common, and this mutation is strongly trans- 
mitted. The breed of swine known as " mule-footed 
hogs " is an example. Horned sheep normally possess- 
ing two horns are sometimes born with four horns. The 
offspring of horned cattle are sometimes born without 
horns, and this variation is strongly transmitted. 

To Hugo De Vries of Amsterdam we owe our present 
definite notions regarding the theory of mutations. While 
such variations were recognized by Darwin and other 

1 Huxley, quoted in Miles' "Stock Breeding," p. 79. 



HEREDITY 153 

investigators, it remained for De Vries to demonstrate 
by scientific investigation the important role played by 
mutations in the evolution of plants and animals. This 
theory undertakes to explain the origin of species by sud- 
den marked variations rather than by continuous or 
fluctuating variations. De Vries* experiments were suc- 
cessful not only in demonstrating clearly the remarkable 
tendency of certain species to vary abruptly, but of even 
more significance was his demonstration of the fact that 
such variations were as surely transmitted as were the 
regular or normal characters of the species. 

It is true, mutations must not be confounded with 
the appearance of freaks or monstrosities among plants 
and animals. Often through arrested development or 
accidental injury during the embryonic existence of ani- 
mals, certain characteristics may become so modified 
that they appear in the form of new characters. Such 
freaks are not transmitted and are not therefore muta- 
tions. The term mutations is used only to designate 
those variations which are heritable. 

144. Kinds of mutations. — Mutations may be addi- 
tions or improvements to the life of organic beings, or 
they may result in diminishing the ability of an animal 
or plant to live and thrive in an ordinary environment. 
De Vries has therefore suggested a classification of muta- 
tions as progressive, regressive and degressive. 

Progressive mutations are those which have contrib- 
uted something entirely new. It is in reality an addi- 
tional character. Attention has already been called 
to cases of variation in which the offspring is provided 
with extra fingers or toes. An example of this form of 
mutation is described by Alexander Graham Bell in the 
ease of multi-nippled sheep. 



154 THE BREEDING OF ANIMALS 

In regressive mutations the animal actually loses 
some hereditary character that it has formerly possessed. 
An animal may be born with less than the normal number 
of digits, and this may be transmitted to offspring. The 
so-called tailless breed of cats is probably descended 
from an individual born without a tail. A polled animal, 
the offspring of horned parents, would also be an example 
of regressive mutation. 

The term degressive has been applied to such varia- 
tions as have existed in the previous ancestral history of 
the animal or plant. When such variations reappear 
after many generations, they are known as degressive 
mutations. 

145. Importance of the mutation theory. — The im- 
portance of the mutation theory to the animal-breeder 
lies in the fact that many of the most important and useful 
qualities present in the domestic animals have probably 
arisen through sudden variations or mutations. Such 
mutations are likely to occur at any time. It is indeed 
probable that such mutations do occur frequently. The 
intelligent breeder who understands the laws of evolution 
will clearly recognize the importance of such mutations. 
The fact that they are certainly transmitted by heredity 
has given to the breeder a most important method in 
the permanent improvement of the domestic animals. 
It is, of course, quite as true that mutations may be 
degressive and thus actually be of less value than the par- 
ent forms. Certain breeds are probably more variable 
than others, and this fact may be both an advantage and 
a disadvantage. It is a desirable condition in that mu- 
tations may occur and some of these may be improve- 
ments over the parent species. Such a tendency to vary 
may be a disadvantage in that the variations may some- 



HEREDITY 155 

times be in the direction of less valuable characters. 
Eventually no breed of animals can be most useful until 
the desirable characters are firmly fixed and reasonably 
certain to be transmitted by inheritance. 

146. Mono-hybrids and di-hybrids. — In all of the 
examples so far used to illustrate the principles of segrega- 
tion and dominance as developed by Mendel, only such 
simple unit characters have been employed as indicate 
clearly the law of Mendel. Such simple contrasting 
characters are known as mono-hybrid. It is easy to 
demonstrate the mendelian hypothesis in the case of 
mono-hybrids. 

But among domestic animals the qualities which have 
made organic beings useful to man are in most part a 
combination of two or more unit characters. In such 
cases it is far more difficult to use the mendelian formula. 
Mendel himself determined the probable application of 
the principle to cases where two different unit characters 
were present. He crossed the wrinkled green peas with 
smooth yellow peas. Manifestly, the number of com- 
binations of characters was greater than when mono- 
hybrids were examined. The proportion of 3 plus 1 is 
the universal result in the Fi generation where single unit 
characters are involved. Mendel found in the case of 
combinations of two unit characters that the mathemat- 
ical statement (3 plus 1)^ (16) represented the true 
result. There would appear sixteen possible zygotes as 
a result of crossing individuals containing two unit 
characters in each of the parents. In the offspring result- 
ing from such crosses the characters would be combined 
in such a manner as to produce sixteen kinds of indi- 
viduals. 

It is apparent that if the number of combinations of 



156 THE BREEDING OF ANIMALS 

unit characters increases, the number of possible different 
individuals produced by crossing similarly increases. 
In the case of tri-hybrids in which three characters com- 
bine, the number of different individuals or zygotes pro- 
duced would be represented by (3 plus 1)^. For the 
purposes of the practical breeder, therefore, little progress 
is possible except in cases where one or two characters 
only are involved. In those cases in which the characters 
involved are made of a combination of many units it is 
first necessary that the important unit characters be 
separated by long-continued breeding; in other words, 
until it becomes homozygous. By such methods, it is 
possible to obtain recombinations, and from the point 
of view of the practical breeder, entirely new characters. 
The mendelian principle may, therefore, in this way be- 
come a powerful instrument in the future improvement of 
domestic plants and animals. 



CHAPTER VIII 
INHERITANCE OF ACQUIRED CHARACTERS 

The normal characteristics of all organic beings may 
be greatly modified by external conditions acting con- 
tinuously upon the organism for a longer or shorter 
period of time. Such modifications may be of so marked 
a character as to cause an apparent departure from the 
average or normal characteristics of the race. Through 
accident, disease or by design, the animal or plant may 
become permanently mutilated. The modifications which 
result from the causes mentioned may make the domestic 
animal or plant more useful to man than the normal 
organism ; the changes may in fact be real improvements, 
and as such it would be very desirable to perpetuate 
them by heredity. Thus the breeder of domestic ani- 
mals, having accurately observed the general fact of 
inheritance of the normal characters, has reasoned that 
such remarkable changes as those often resulting from 
use or disuse, favorable environment or mutilations must 
be transmitted with equal force. 

147. Belief in transmission of acquired characters. — 
The literature of the ancients indicates that the philos- 
ophers of that period believed in the inheritance of 
acquired characters. Aristotle mentions the transmission 
of the exact shape of a cautery mark. At a much later 
period Lamarck elaborated his theory of variation and 
selection which took for granted that all modifications 

157 



158 THE BREEDING OF ANIMALS 

resulting from use and disuse and the effects of environ- 
ment were transmitted by heredity.^ 

Among those who have failed to find satisfactory 
evidence of the inheritance of modifications must be 
mentioned Kant, Blumenbach, and later Galton, Weis- 
mann, Ray Lankester and practically all the leading 
biologists of modern times. 

148. Practical breeders believe in transmission of 
acquired characters. — There is a widespread belief 
among the breeders of domestic animals that acquired 
characters are inherited. To the practical breeder of 
dogs who has observed the sensitive reaction of the fox 
hound to the scent of the fox, or the alertness of the setter 
or pointer in the presence of a fresh bird track, it is diffi- 
cult to find a satisfactory explanation for existing facts 
without assuming that the results of the training of a 
dog to some extent must be transmitted. Extreme speed 
in running and trotting horses is the result of training 
and exercise. The offspring of parents who have acquired 
extreme speed through training and exercise are more apt 
to possess the ability to acquire similar extreme speed 
than the offspring of parents who have not been trained. 
The practical breeder concludes, therefore, that the ac- 
quired speed must be transmitted. 

There are many breeders of beef cattle who firmly 
believe that by maintaining the breeding animals in high 
condition, the calves will have a more pronounced devel- 
opment of those characters which are recognized as 
belonging to the beef type than will the calves of parents 
which are maintained on a low plane of nutrition. 

The breeder is an accurate observer, and there can be 
no question that his facts are generally correct in this 

1 Thomson, "Heredity," p. 170. 



INHERITANCE OF ACQUIRED CHARACTERS 159 

instance as in many others. But the biologist could 
easily explain the facts cited upon wholly different grounds. 
The fact that the trotting horse parents could be developed 
to high speed indicated clearly that they had inherited a 
capacity for such development. The offspring inherited 
the same capacity and under the same favorable condi- 
tions would develop the same speed. The breeder of 
beef cattle is in general correct in his practice when he 
maintains his breeding animals on a high plane of nutri- 
tion, not because such treatment in any way influences 
the fundamental constitution of the germ-plasm, but 
because this is a satisfactory method of determining which 
breeding animals possess the fattening tendency. Those 
parents that show the capacity for rapid and economical 
fattening are preserved and the unthrifty are eliminated 
from the breeding herd. The high plane of feeding is a 
method of selection. 

149. Nature and nurture. — The nature of an animal 
is determined by heredity. What an animal may become 
is limited by its inheritance. What an animal actually 
becomes is often largely determined by the use made of 
its inheritance. The individual may inherit great possi- 
bilities, but these may never be realized because unde- 
veloped. The characteristics of an individual, then, are 
the result of both nature (heredity) and nurture (develop- 
ment). 

The tremendous importance of nurture to the indi- 
vidual is demonstrated by numerous examples. The 
untrained trotting horse may have inherited the same 
possibilities for development as his stable mate, but 
because of superior opportunity through skillful training 
the latter makes a new trotting record while the former 
achieves nothing. 



160 THE BREEDING OF ANIMALS 

The most notable examples of acquired development 
are to be found in the human family. Through the life- 
time of a man the mental and physical qualities may be 
greatly modified. An individual may acquire great 
mental power. Such acquirement may have been 
achieved under very great difficulties. The particular 
kind of mental efficiency represented by the develop- 
ment of such an individual may be an exceedingly desir- 
able characteristic of the greatest value to the human 
race. Its transmission by heredity would be desirable 
for the good of the race. Can such acquired characters 
or habits be transmitted? The answer to this question 
is important to the development of the human race. It 
is likewise of the greatest economic importance to the 
breeder of domestic animals. In the domestic animals 
the highly artificial characters possessed by the improved 
forms of cattle, horses, sheep and swine are very largely 
due to the development or good handling to which these 
animals have been subjected. If the results of the 
high degree of development of one generation are to 
fundamentally influence the characters of the next, then 
a new significance will be given to the effects of environ- 
ment. 

150. What are acquired characters ? — The use of 
the term acquired characters to indicate entirely different 
facts has given rise to some confusion in the consideration 
of this subject. In one sense no character is ever trans- 
mitted. Only the determiners which give direction to 
the developing characters of the animal or plant are 
actually inherited. The characters themselves develop 
out of and are determined by the fundamental constit- 
uents of the germ substance. Thus the appearance of 
the secondary sexual characters of the male at puberty 



INHERITANCE OF ACQUIRED CHARACTERS 161 

are not acquired characters in the biological sense. Ac- 
quired characters are modifications of the somatic cells 
which are induced by environment, use or disuse, acci- 
dents or any other influences acting upon the body-cells 
in such a way as to change their normal development. 
According to Weismann, if the modifications are the result 
of the presence of determiners in the germ-plasm, then 
they are not properly designated as acquired characters. 

151. Somatoplasm and germ-plasm. — From the view- 
point of the biologist, all organic beings which reproduce 
sexually are differentiated into two very clearly defined 
groups of cells : the somatic group, which includes all 
the cells concerned in the processes of nutrition, includ- 
ing digestion, absorption and assimilation; the nerve 
cells and all other cells involved in the physiological 
activities of the organized being, except the reproductive 
cells. 

Distinct and apart from the soma- or body-cells are 
the germ-cells, the function of which is to provide for 
the reproduction of the species. Weismann was the 
first to point out clearly the very sharp division between 
the fundamental organization and function of these two 
groups. The somatoplasm has its origin in the germ- 
plasm, and the direction of its development is controlled 
by the determiners in the germ-plasm, but the germ- 
plasm is not influenced in any fundamental way by the 
somatoplasm. The soma is to be regarded in the nature 
of a habitat for the successful activities of the germ-cells. 
In a sense, the somatoplasm has no more influence upon 
the developing germ-cells harbored within the soma than 
does the soil upon the trees which may develop from 
the seeds planted on its surface. 

The germ-plasm is continuous. It is a part of the 

M 



162 THE BREEDING OF ANIMALS 

germ-plasm of the preceding generation. If this dis- 
tinction and differentiation is kept clearly in mind, it 
will help materially in the discussion of the inheritance 
of acquired characters. If we accept Weismann's def- 
inition of acquired characters, that they are somatic 
modifications which do not have their origin in the germ- 
plasm, we have to discuss only such somatic modifications 
as may be acquired by the animal during its lifetime. 

152. Examples of acquired characters. — Among the 
common causes of the changes in the soma must be 
grouped environment, including food and climate; use 
and disuse of parts ; disease and accidents. Each of 
these acting separately or all of them acting together may 
cause profound changes in the external form and develop- 
ment of plants and animals. 

153. Food supply. — Perhaps no other single environ- 
mental influence is responsible for such profound changes 
in the external form of plants and animals as the food 
supply. The Kerry cattle of Ireland are a diminutive 
race of cattle which have been long subjected to condi- 
tions of scant supply of innutritions food. Their size 
and hardy character must be regarded as a more or less 
successful adaptation to their environment. When young 
calves of the Kerry breed are surrounded with conditions 
in which they are supplied with a generous and nutri- 
tious food, they increase in size and come to maturity 
at an earlier age.^ 

The Shetland pony in the barren islands of Shetland, 
gathering a scant subsistence from the inferior grasses 
and forage plants, develops into one of the most diminu- 
tive races of horses known to man. The same race of 
horses transplanted to the fertile regions of Great Britain 

1 Miles, "Principles of Stock Breeding," p. 100. 













- "^JSLAlJv.^^^^BPMlft 


4 


j 


^ 


1 








1 


^^Uj^ %£ ':7l 


^ 








1 


rmk^. 






IIJII^""", / 




1 








Iflpi^''^^^ 




I 


^^^^^^^E- 






Sp" 


. '^^ 


1 


". s.'^!^8 


J^* ^ V 


MM^^^' ^ 






Plate VII. — Upper. Ration not restricted. Fed for rapid growth 
and development from age 90 days. Age 716 days, weight 1401 pounds. 
Lower. Ration greatly restricted. Age 777 days, weight 512 pounds, 
height 121 cm. 



i 





Plate VIII. — Upper. Ration not restricted. Fed for rapid growth 
and development from age 90 days. Age 336 days, weight 875 pounds. 
Lower. Ration partially restricted. Fed for normal but moderate 
growth and development. Age 780 days, weight 813 pounds, height 
128 cm. Compare with Plate VII. 



INHERITANCE OF ACQUIRED CHARACTERS 163 

or America increases in size as the result of a better food 
supply. 

Woltereck, by changing the food supply only, in hyalo- 
daphnia, succeeded in changing the percentage of the 
height of the head to that of the body from 40 to over 90. 

The remarkable influence of the amount of food supplied 
to an animal during its development in modifying the 
somatic cells and changing the external form of animals, 
is well illustrated by the unpublished results of an experi- 
ment conducted at the Missouri Experiment Station.^ 
In this investigation, the animals were maintained for 
long periods upon different planes of nutrition. 

For the purpose of this investigation the animals were 
divided into three groups. Group one (see Plates VII, 
VIII and IX) was supplied with a generous ration cal- 
culated to furnish to the animal all the nutrients it 
could utilize, and produce the maximum growth and 
development, including the laying on of fat. The treat- 
ment given to group one resulted not only in very 
rapid growth and development, but as the excessive 
feeding was long continued, the animals laid on unusual 
and excessive amounts of fat. 

The ration supplied to group two (see Plate VIII, 
lower) was intended to provide such a quantity of food 
as was sufficient to produce strong, healthy growth and 
development, but insufficient for laying on any consider- 
able amount of fat. This ration resulted in normal, 
healthy growth, but the food supplied was constantly 
below the desires and appetites of the animals. There 
was no time during the experiment at which the animals 
would not have consumed more food. 

^ Waters and Trowbridge, Unpublished Data from the Mis- 
souri Experiment Station. 



164 THE BREEDING OF ANIMALS 

Group three (Plate VII, lower) was limited markedly in 
the amount of food which the animals were permitted to 
consume. The scant ration given to group three did not 
prevent the animals from growing, but it did prevent the 
animals from making a normal growth, and prevented the 
normal deposition of fat within the body tissues, which 
seems to be a favorable factor, in inducing healthy growth 
and development. 

The illustrations represent typical animals in the three 
groups. These illustrations give a general impression 
of the changes in body form which are readily apparent 
to the eye, resulting from the methods of treatment of 
these various groups. 

154. Influence of the amount of food on body weight. — 
A record of the changes in the body weight of an animal 
is not the most accurate measure of the influence of any 
environmental factor, but it is sometimes very useful, 
and often the best measure available. In this experi- 
ment, animal 501, which was fed for forty-seven months 
on a full ration, attained in that time a total weight of 
1965 pounds. Animal 512, fed a medium ration for 
forty-eight months, attained a weight during that period 
of 1224 pounds. Animal 500, belonging to the low-fed 
group, weighed, at the end of the forty-eight months' feed- 
ing, 1042 pounds. The differences observed in these 
animals must be due entirely to the differences in the 
amount of food supplied, as they were subjected to iden- 
tical conditions in all other respects. The experiment 
would have been still more valuable if the animals in the 
three groups had been fed on the different rations from 
birth. As a matter of fact, the animals in all the groups 
were generously fed during the first five months of their 
lives. 




h:^-s^^^. 




Plate IX. — Upper. Steer 527 weighing 200 pounds at age 120 
days. Fed maximum ration for rapid growth and development from 
age 90 days. Lower. Same, weighing 1453 pounds at age 27 months ; 
rations not restricted. 



INHERITANCE OF ACQUIRED CHARACTERS 165 

155. Food supply and body changes. — All the evi- 
dence available points to the fact that the domestic ani- 
mals have inherited not only a tendency to reach a cer- 
tain size and form, but that they have inherited a strong 
tendency to attain a given size at a certain age. Thus, 
in these investigations at the Missouri Experiment 
Station, there is evidence to show that the animal organ- 
ism makes desperate efforts to grow, even when the food 
supply is greatly limited. In one case a calf nine-and- 
one-half months old was fed a limited ration which 
resulted in a loss of weight amounting to 82 pounds in 
six months. During the same period this animal in- 
creased 8.1 per cent in height and 14.1 per cent in length 
of head.^ 

156. Influence of limited food supply from birth. — 
The amount of food supplied to a growing animal in a 
large measure determines not only its ultimate develop- 
ment, but the rate at which the animals grow. In another 
investigation at the Missouri Experiment Station,^ three 
animals were fed a full ration, a medium ration and a 
scant ration, respectively. Animal number 527 (Plate VII, 
upper) given a full ration, increased in weight rapidly, and 
at the end of 789 days weighed 1453 pounds. Animal 559 
(Plate VIII, lower), given a medium ration intended to 
produce a normal growth, but not a fattening ration, at 
the end of 780 days weighed 813 pounds. Animal 551 
(Plate VII, lower) , given a scant ration, weighed at 777 days 
512 pounds. It is, of course, possible that in these experi- 
ments the differences in body weight may be due to the 

^ Waters, Proceedings of the Society for the Promotion of Agri- 
cultural Science, 1908. 

2 Waters and P. F. Trowbridge, Unpublished Data of the 
Missouri Experiment Station. 



166 THE BREEDING OF ANIMALS 

amount of fat deposited in the tissues rather than to differ- 
ences in the development of the skeleton and muscular tis- 
sues. The very great differences in weight noted are of the 
greatest significance if they represent differences in the 
fundamental skeletal and muscular tissues of the body. 
If they represent alone differences in the amount of fat, 
they are not so significant. The height of each animal 
as observed seems to indicate clearly that not only is 
the amount of fat deposited in the tissues directly 
determined by the amount of food available, but the 
skeletal growth also is profoundly influenced by the food 
supply. 

There can be no question but that limiting the amount 
of food supplied to young animals has a profound influ- 
ence upon the rate of growth as well as its ultimate size. 
This influence is to be found in smaller skeleton, probably 
arrested development of the muscular tissues, and a much 
smaller percentage of fat. 

157. Telegony. — There was a time when eminent 
biologists and practical breeders firmly believed that the 
influence of the sire was not confined to his immediate 
offspring but the mother herself was in some manner so 
impressed with the characters of the sire that her subse- 
quent progeny sired by entirely different males might 
take on the characters of the former sire. " The act of 
fecundation is not an act which is limited in its effect," 
says Agassiz,^ " but that it is an act which affects the 
whole system, the sexual system especially; and in the 
sexual system the ovary to be impregnated hereafter 
is so modified by the first act that later impregnations 
do not efface that first impression." Darwin supported 
his belief in telegony by citing many cases among plants 

^ Massachusetts State Board of Agriculture, 1863, p. 56. 



INHERITANCE OF ACQUIRED CHARACTERS 167 

of '' direct action of the male element on the mother 
form." He remarks further that " the male element 
not only affects, in accordance with its proper function, 
the germ, but the surrounding tissues of the mother 
plant." 

Spencer likewise admitted the probability of the pas- 
sage of the germ-plasm from the growing embryo into the 
maternal tissues and thus to the germ-cells. Weismann 
held that if any such influence in reality existed, it could 
be explained only on the theory that some of the sperm- 
cells of the male penetrated to the undeveloped ova and 
there accomplished a partial impregnation. Some prac- 
tical breeders, of horses and dogs particularly, were so 
thoroughly impressed with the possibility of such an 
influence that they would not buy a highly bred animal 
that had borne offspring to another breed, believing that 
such a female could not be trusted to breed true. Some 
farmers in the mule-breeding districts have reported 
that horse foals from mares which had previously pro- 
duced mules, sometimes possessed " mulish characters." 
These characters which are commonly possessed by the 
hybrid appearing thus in pure horse foals were supposed 
to have come about through the influence of the jack on 
the mother at some previous mating. 

158. The Lord Morton mare. — One of the most 
striking cases of supposed infection was reported to the 
Royal Society ^ by Lord Morton in 1820. 

The essential facts are discussed by Darwin.^ In the 
year 1815 Lord Morton bred a seven-eighths Arabian 
mare of chestnut color to a quagga. The resulting 

^ Philosophical Transactions, 1821, p. 21. 
2 Darwin, "Animals and Plants under Domestication," 
vol. I. 



168 THE BREEDING OF ANIMALS 

offspring was a true hybrid having the same color 
and in other characters resembhng the sire. Later in 
1817, 1818 and 1821 the same mare was bred to a black 
Arabian stallion and from each mating produced a healthy 
foal which in every case was marked with stripes like 
the quagga sire, and resembling the sire also in the char- 
acter of the mane. Lord Morton, in describing the 
particular resemblances of these foals, says : " Both in 
their color and in the hair of their manes they have a 
striking resemblance to the quagga. Their color is 
very marked, more or less like the quagga in a darker 
tint. Both are distinguished by the dark line along the 
ridge of the back, the dark stripes across the forehead 
and the dark bars across the back part of the legs." ^ 
The existence of stripes or bars on young foals is not 
uncommon, and their presence on the offspring of the 
Lord Morton mare may be explained on other grounds 
than the assumption that they were caused by the influ- 
ence of a previous impregnation of the Arabian mare by 
the quagga sire. 

159. The Penycuik experiments. — The possibility of 
tracing to some other source the real or fancied resem- 
blances of the Arabian foals to the quagga sire of a pre- 
vious mating, led Cossar Ewart to make a thorough inves- 
tigation of the so-called infection theory. At Penycuik 
in 1895 Ewart repeated as closely as possible the breed- 
ing experiment of Lord Morton. In these experiments 
thirteen mares of varied colors and breeds produced a 
total of sixteen foals to a Burchell zebra. The same mares 
later produced twenty-two foals by Arab, Thoroughbred 
and Highland stallions. Ewart, in describing a typical 

1 Ewart, Bureau of Animal Industry Report, 1910, U. S. 
Dept. of Agr. 



INHERITANCE OF ACQUIRED CHARACTERS 169 

result, says : ^ " The first hybrid was born August 12, 
1896, the dam being Mulatto, a black Highland pony 
lent by Lord Arthur Cecil." 

" In 1897 Mulatto had a foal to Benazrek, a gray Arab 
stallion. As this subsequent foal of Mulatto was indis- 
tinctly striped, I was at first inclined to believe she had 
been infected by her first sire, the zebra Matopo ; but 
when more richly striped pure-bred foals were obtained 
later by Benazrek out of Highland mares which had never 
even seen a zebra, it became evident that Mulatto af- 
forded no evidence in support of the infection doctrine. 

" Lord Morton's quagga counted for so little in the 
hybrid out of the chestnut Arab mare that its right to 
be regarded as a hybrid has been questioned. Matopo, 
however, proved so impressive that all his hybrid offspring 
plainly indicated their descent from a richly striped 
zebra. 

" On the other hand, the subsequent foals (by Arab 
and other stallions out of the mares which proved fertile 
with Matopo) differed so profoundly from hybrids (even 
when, as was sometimes the case, they had bars on the 
legs and faint stripes across the withers) that they afforded 
no evidence that the first male influences ' the progeny 
subsequently borne by the mother to other males.' " 

Baron de Parana in Brazil produced many zebra 
hybrids also from a true Burchell zebra, later rearing pure 
horse foals from mares that had previous zebra hybrids. 
In no single case did the stripes which did sometimes 
appear resemble closely the striping of the zebra. 

A somewhat extended inquiry by Romanes in 1893 

1 Ewart, "The Principles of Breeding and the Origin of Do- 
mesticated Breeds of Animals," Report of the Bureau of 
Animal Industry, U. S. Dept. of Agr., 1910. 



170 THE BREEDING OF ANIMALS 

in British and American live-stock journals developed 
the fact that telegony is not as generally believed among 
breeders of the present day as has been generally reported. 
Sir Everett Millais, as the result of over fifty experiments 
with mammals and birds, found no conclusive evidence 
of infection. 

Evidences of telegony, if it exists at all, ought to be 
easily collected in those regions where the production of 
mules is common. Darwin says,^ '' It is worthy of note 
that farmers in South Brazil (as I hear from Fritz Miiller) 
and at the Cape of Good Hope (as I have heard from two 
trustworthy correspondents) are convinced that mares 
which have once borne mules when subsequently put to 
horses are extremely liable to produce colts striped like 
a mule." 

These conclusions are not supported by Baron de 
Parana,^ who reports, " I have many relatives and friends 
who have large establishments for the rearing of mules 
where they obtain 400 to 1000 mules in a year. In all 
these establishments, after two or three crossings of the 
mare and ass, the breeders cause the mare to be put to a 
horse because they believe that unless the mares are 
changed after producing three mules they become sterile. 
In all these establishments a pure-bred foal has never 
been produced resembling either an ass or a mule." 

160. Telegony and mule hybrids. — In the horse- 
breeding districts of Missouri, large numbers of mules 
are produced annually. Many of the mares which have 
produced one or more mules are later bred to stallions 
and thus become the dams of horse foals. The jack 
and the stallion differ so widely in many important 
particulars that any marked tendency of horse foals to 

1 Report of the Bureau of Animal Industry, 1910, p. 123. 













■HM|^^^BH 


^^^A 




^^t^^^^^e C^ rt^^BL.a^^H 


^^^^^^^^^^^^^KH 


^^^^^^Kli.^ 


j|»C«^»? 




^^^^^^^^^^^^^^^^^Kml 


D^^^^^^Htl^l 


^Hl^ ' 


Hm j'^IH.'' gjl^^^l 


I^^^^^^^^^^^H 


^j^^^^^l 


^Hk 


KKm'^'Iiv'' ^^^^^^ 


^^^^^^^^^^^H^^H 


I^^^H^^Hl 


^Ht 


mt ^w ^r\ 


^H ^^^!^^^^^^^^», , • 


^HH 


v 


m -^^^ W 


1 


^t^m 1 


P^ii''' 


Mjl^ ^^^^SEBWkk:^ --s^^ III^B 


mO„ 


^H^E^^^^Ir 


V^ nHL 




"■m/-jf *' ''f\'^ *~ ' ''*'<^'? !^ 


IIBJ 


• -r* 




<JIHiMHMn|HHHH 


URk^ 


^!W^* ■L 


..y^^rV'- 




fet>f%/.*'''' 


.A 




Plate X. — Upper. Illustrating a condition favorable to the 
appearance of telegony in horses. This mare produced seven mule 
foals and then the mare shown below. Lower. The dam of this mare 
produced seven mule foals previous to the birth of this animal. 




Plate XI. — Upper. "Hallie," the eleventh foal of the dam 
"Maude" — the latter having previously given birth to ten mule foals 
in succession. Lower. "Maude," dam of "Hallie," produced ten 
mule foals previous to birth of "Hallie." 



INHERITANCE OF ACQUIRED CHARACTERS 171 

resemble a previous jack sire would be quickly observed. 
The writer ^ and C. B. Hutchison made an investigation 
of a large number of the horse offspring of mares which 
had previously foaled mule progeny from jack sires. 
Many of the horse foals examined were from mares that 
had produced more than one mule. In one case a mare 
had given birth to thirteen mule foals in succession and 
had then produced a horse foal. Many similar cases 
gave opportunity to observe a number of examples in 
connection with which full and favorable opportunity 
was present for the display of the influence of a previous 
impregnation. If, as some believe, the influence of a 
previous impregnation is cumulative and the dam becomes 
more and more completely infected by successive matings, 
these results should give an excellent opportunity to 
obtain some evidence on the theory of " infection " or 
'' saturation." 

A total of 168 mares were located that had given birth 
to mule foals and later had produced horse foals. Of 
this number 108 produced their first foal to a jack and 
later gave birth to horse foals. Among the number were 
forty mares that produced their first foals to a stallion, 
later producing mule foals and then again horse foals. 
The remainder were bred in a somewhat irregular manner, 
but all were alike in having produced horse foals following 
mule foals. The number of mares producing one or more 
mule foals each followed in every case by horse foals was 
as follows : Eighteen males produced one mule foal each, 
followed by a horse foal ; twenty-two mares produced 
two mule foals each, followed by a horse foal; twelve 
mares produced three mule foals each, followed by a 

1 Mumford and Hutchison, Unpublished Data of the Missouri 
Experiment Station. 



172 THE BREEDING OF ANIMALS 

horse foal; twenty mares gave birth to four mule foals 
each, followed by a horse foal; eight mares gave birth 
to five foals each, and later to horse foals; ten mares 
observed produced six mule foals each, and afterward 
gave birth to horse foals; seven mares produced seven 
mule foals followed by horse foals; G.ve mares produced 
horse foals after having foaled eight mules each, two mares 
dropped ten mules each, followed by horse foals; while 
one mare produced ten mule foals and then a horse foal 
and one mare was bred to a stallion and produced a healthy 
horse foal after having given birth to thirteen mule foals 
in succession. 

161. Example of horse foals. — The horse foals from 
these mares were carefully examined and measured for 
the purpose of discovering any possible resemblances 
to the previous jack sire from which mules had been 
produced. The chief external characters which dis- 
tinguish the mule from the horse are the size and form of 
the ears, head, feet, legs, body, mane, tail, disposition and 
voice. 

The illustrations of dams and offspring give a fairly 
adequate idea of the generally uniform nature of the 
results which were found throughout the investigation. 

In Plate X, lower, is shown the yearling offspring of a 
mare (Plate X, upper) that had previously produced seven 
mule foals and then gave birth to the animal shown in the 
illustration. A careful examination of the characters in 
which mules and horses differ showed that the offspring 
in this case had small, rather short, smooth head, small, 
short, pointed ears, a broad flat foot and rather broad 
hips and loins, with a well-rounded body. None of the 
characters of this yearling colt suggested in the slightest 
degree any evidence that it had been influenced by the 





Plate X^TT tj 

foals from same dam'"^i„3'''"TL*H!,°'"'J' '?!"' '""""''"e «sht -nule 




Plate XIII. — Upper. "Crewdson." A condition favorable to the 
appearance of telegony. Previous to the birth of this mare her dam (Kate) 
had given birth to eleven mule foals in succession. Lower. "Kate," 
mother of eleven mule foals in succession, and later of "Crewdson." 



INHERITANCE OF ACQUIRED CHARACTERS 173 

fact of its dam having previously produced seven mule 
foals. 

*' Sallie " (Plate XII, upper) was foaled by a saddle bred 
mare fifteen years old and was the ninth foal from this 
mare. The previous eight foals were all mules. The mare 
" Sallie " was characterized by a small refined head of 
good quality, a small, short and pointed ear, rather scanty 
mane and tail, fine bone, broad and rounded foot and quiet 
and gentle disposition. 

The mare " Hallie " shown in Plate XI was sired by a 
Standardbred stallion from the dam " Maude " (Plate XI, 
lower). Maude had previously given birth to ten female 
mule foals. At two years of age " Hallie " weighed 800 
pounds, was fifteen hands high, had a short, small, refined 
head, short pointed ears, heavy and long mane and tail, 
broad flat foot and a rounded body. All of the external 
characters of this mare were clearly horse characters and 
not mule characters. There was no suggestion of any 
resemblance to the mule in any of its characters. 

'' Crewdson " (Plate XIII, upper), three years old, was 
sired by a Hackney stallion from the dam " Kate " (Plate 
XIII, lower), the latter having given birth to eleven mule 
foals followed by the horse foal " Crewdson." This 
animal was sixteen and one-half hands high and weighed 
1000 pounds. The head was small and narrow, ear 
short and small, mane and tail medium heavy, foot broad 
and flat. " Crewdson " was characterized by a heavy 
mane and tail, small ear, refined head and broad rounded 
foot. 

The cases cited and the illustrations used were selected 
because it was assumed that if the influence of a previous 
impregnation was likely to be exhibited at all it would 
appear in those dams w^hich had produced a large number 



174 THE BREEDING OF ANIMALS 

of mules followed by horse foals. No such evidence could 
be discovered. The 168 horse offspring from mares 
which had previously produced from one to thirteen mule 
foals each, gave no visible evidence of the existence of 
telegony. The external characters of the mule hybrid 
and the horse differ so widely in many important partic- 
ulars that even a slight influence which might come 
through a previous sire should have been measurable. 

It is true that the evidence is all negative, but it is 
nevertheless valuable because of the peculiarly favorable 
opportunity for the influence of telegony to assert itself. 
It is also interesting to note in this connection that a 
belief in the possible influence of a previous impregnation 
is by no means universal among practical breeders, if 
we may judge from the statements of farmers in the mule- 
breeding districts of Missouri. Very few breeders believed 
in the existence of telegony. Those who admitted their 
belief in the possibility of infection were unable to cite 
authentic instances. 

162. Possibility of influence from a previous impregna- 
tion. — If the influence of the male is not confined to 
his immediate offspring but is extended to the mother 
in such a way that other progeny by other males may 
display some of the characters of the former male, then 
such influence must come about in one of two ways. 
The body (soma) of the mother herself may be so funda- 
mentally changed by acquiring the characters of the male 
that she transmits such influence to her succeeding off- 
spring sired by other males. The spermatozoa of the 
male may not only fertilize the fully mature and thus 
susceptible ovum but may travel through the generative 
organs of the female and eventually reach the ovaries 
where the developing and immature eggs might be so 



INHERITANCE OF ACQUIRED CHARACTERS 175 

influenced that at a later time the fully fertilized egg 
would exhibit the results of fertilization by spermatozoa 
from two different males. The possibility of such double 
fertilization is extremely remote. The known facts 
regarding the successful fertilization of the Qgg are all 
against such an hypothesis. The ^gg is probably not 
susceptible to fertilization by the sperm except during 
a comparatively brief period which is coextensive with 
the heat period in the domestic animals. The immature 
ova still structurally a part of the ovary are not in proper 
condition to be fertilized. The probabilities are all 
against any such influence from this source. 

Is it possible that the characters of the male may 
become impressed upon the pregnant female through the 
influence of the foetus ? If the body (soma) of the female 
is influenced in this way is this influence of such a nature 
that it can be impressed upon the embryo in the uterus ? 
If it can, then the characters of a previous male may 
affect the later offspring by other males. Here again we 
must admit that the period of gestation may change the 
body of the mother to some extent, but it is extremely 
improbable that such change influences the offspring in 
any hereditary sense. As Rabaud ^ says, " Gestation 
naturally produces in the female a modification which 
we must suppose to be to some extent permanent. As 
a consequence, the female which produces a second off- 
spring is no longer the female that produced the first 
offspring; whether the two gestations be due to the 
same male or to two different males, the foetus of the sec- 
ond gestation evolves in conditions different from those 
surrounding the foetus of the first gestation. But it does 

1 Etienne Rabaud, "Telegony," The Journal of Heredity^ 
vol. 5, p. 389. 



176 THE BREEDING OF ANIMALS 

not undergo in any way the influence of the first male; 
in reality, what takes place is as if two different females 
were involved, mated with the same male or with two 
different males." 

The conclusion seems very plain that the practical 
breeder has little interest in the subject of telegony. 
While it is difficult or impossible to prove by direct 
experiment that telegony does not exist, it is also true 
that no one by direct experiment has ever been able to 
produce any result which could not be explained on some 
other basis than that of telegony. All of the supposed 
cases of telegony can likewise be explained on some other 
basis than the assumption that a previous impregnation 
is lasting in its effect and may influence subsequent off- 
spring. 

163. Xenia in animals. — In plants the effect of cross- 
pollination in certain cases is to be observed in the fruits. 
Gardeners have long believed that the watermelons and 
citrons should not be planted in near-by locations because 
the pollen from the citron would injure the quality of 
the melon. Such injury really does not occur in this 
particular case but similar effects are present in other 
plants. When ordinary white corn is fertilized with 
pollen from a black variety, the grains so pollinated are 
black or mottled while other grains on the same ear are 
white. An explanation for this phenomenon is to be 
found in the fact that there are two cell nuclei in the ovum 
and two nuclei in the pollen cell. The primary nuclei 
of the two cells unite to form the daughter nucleus of the 
new cell. The two secondary nuclei likewise unite in 
the formation of the endosperm. In the case of cross- 
pollination of black and white corn it is the color of the 
endosperm which exhibits the influence of the crossing. 



INHERITANCE OF ACQUIRED CHARACTERS 177 

Among mammals the highly imaginative idea has been 
suggested that the influence of the male on the female 
(infection) may in turn be passed on to a later male mated 
with the infected female. A highly successful breeder 
of Shorthorn cattle in England pointed out to the author 
a pure-bred white cow with red ears from a registered 
sire and dam. This cow was marked like the wild white 
cattle of Chillingham Park, and her owner ascribed her 
markings to the fact that her dam had once dropped a 
calf from a Chillingham bull. The cause of the peculiar 
markings of the cow in this case could not have been 
derived in the manner described. The case is cited here 
only as an example of the highly improbable notion that 
there is some relation between the phenomena of teleg- 
ony and xenia. Xenia among mammals is unknown. 

164. Xenia among poultry. — Many breeders of poultry 
have believed that the eggs of the domestic fowl may be 
influenced in size, form and color by the male bird. 
Observations by Nathusius and later by Holdefleiss ^ 
gave evidence of paternal influence on the color of the 
eggshell. Holdefleiss mated Plymouth Rock hens with 
a Leghorn cock. The Plymouth Rock uniformly lays 
brown eggs while the Leghorn lays a pure white egg. 
The eggs deposited by the Plymouth Rock hens from this 
mating varied in color from dark brown to white. The 
evidence seemed so clear to the investigator that he was 
led to conclude that " The color of eggshells shows the 
influence of the paternal strain ; there is therefore evidence 
of xenia." More recently Walther ^ of Giessen after a 
series of careful experiments has reported results which 

1 Holdefleiss, " Berichte aus dem biologische Lab.," Univ. Halle, 
1911. 

2 Walther, "Landwirthschaftliche Jahrbiicher," 1914. 

N 



178 THE BREEDING OF ANIMALS 

do not confirm those of Nathusius and Holdefleiss. Wal- 
ther's investigations included not only color but also 
size, form and glossiness. His conclusions were that 
the paternal parent has no influence on the size, shape 
and glossiness of the eggs. His results on the color of 
eggs are not conclusive but tend to discredit the theory 
of xenia in fowls. From all the evidence available, it 
would seem that the possibility of xenia in fowls is not 
satisfactorily determined, and further investigation is 
needed to settle this supposed influence of the male bird 
on the color of eggs. 

OBJECTIONS TO THE THEORY THAT ACQUIRED CHARACTERS 
ARE TRANSMITTED 

The trend of opinion of modern biologists has been 
further and further away from the belief in the possibility 
of the inheritance of acquired characters. As our knowl- 
edge of cellular biology has increased and we have been 
able to study the mechanical processes which are concerned 
in reproduction and heredity, it has become more and 
more apparent that Weismann's view of the essential 
separateness of the soma-cells and germ-cells is sub- 
stantially correct. 

165. No mechanism for the inheritance of acquired 
characters. — There is no mechanism by means of which 
somatic modifications may impress themselves funda- 
mentally upon the germ-plasm. In fact, the develop- 
ment of the soma-cells is made possible by determiners 
in the germ-cell. The very fact that the soma-cells 
have been able to respond to external influences and 
develop in a direction somewhat different from the average 
of the species is sufficient evidence that the determiners 



INHERITANCE OF ACQUIRED CHARACTERS 179 

which were responsible for the tendency of the organism 
to develop in the given direction were already present 
in the germ-plasm. As Walter aptly remarked, " Not 
only the development of the race which we call evolution, 
but also the determination of the individual in heredity, 
is a chain of onward-moving sequences like the succession 
of events in history. It is hard to see how recent events 
can influence preceding events. It is hard to see how 
the water that has gone over the dam can return and 
affect the flow of the river upstream in any direct way. 
It is likewise hard to see how differentiated somatoplasm, 
which represents the end stage of a successive series of 
modifications, can make any definite impress upon the 
original germplasmal sources from which it arose." ^ 

Even Darwin found difficulty in believing in the inheri- 
tance of acquired characters. His theory of pangenesis 
which assumed that each somatic cell added to the cir- 
culation a minute granule which later found its way to 
the germ-plasm is not substantiated by later investiga- 
tions. 

The evidence presented to prove that somatic modi- 
fications are actually transmitted from parent to offspring 
is not conclusive. It is certain that acquired characters 
cannot be transmitted unless the germ-plasm has been 
definitely changed by reason of somatic influence. The 
evidence of such influence upon the germ-cell is entirely 
negative. Definite experiments carefully planned for 
testing the possible effect of such influence have been 
inconclusive. 

166. The inheritance of disease. — The earlier writ- 
ings on animal breeding contain numerous references to 
the possibility of inheritance of disease. Many examples 

1 Walter, "Genetics," 1913, p. 85. 



180 THE BREEDING OF ANIMALS 

are recorded among the domestic animals of supposed 
cases of the heredity of pathological conditions. Among 
the diseases which have been regarded as hereditary are 
tuberculosis, melanosis, broken wind, specific ophthalmia, 
blindness, spavin, ringbone, curb and many other diseases. 
The discussion of the transmission of diseased conditions 
of the organism brings forward again the entire question 
of the possible inheritance of acquired characters. In 
general it may be said that recent researches in biology 
have resulted in demonstrating that many diseases which 
were formerly regarded as transmissible are no longer 
believed to be transmitted through inheritance. This 
certainly applies to all diseases which are contracted 
after birth. Some diseases which are the result of a 
definite variation in the germ-plasm will of course be 
transmitted. We must therefore clearly distinguish 
between inborn disease and acquired disease. Certain 
diseases or defects are undoubtedly transmitted from 
parent to offspring. Whenever such defects represent 
changes in the germ-plasm, then such defects will be as 
certainly transmitted as any other character of the animal. 

Such defects which may be transmitted are deaf- 
ness, color-blindness, idiocy and possibly rheumatism, 
gout and insanity. In the latter diseases their apparent 
transmissibility may be the result only of a predisposition. 

167. Acquired diseases. — Many diseases of the do- 
mestic animals are acquired after birth. A large number 
of pathological diseases are due to infection. All such 
diseases are no more certainly transmitted than are other 
acquired characters. Tuberculosis is the result of infec- 
tion by a specific germ and this germ may be acquired 
under certain conditions by the animal organism. In 
the case of bone diseases of horses, which were for a long 



INHERITANCE OF ACQUIRED CHARACTERS 181 

time held to be inherited, it is probable that the develop- 
ment of such unsoundness is due largely to the action of 
external factors. In other words, they are acquired. It 
is true, however, that certain individual animals or 
families are much more subject to bone disease than other 
families. In such case we must recognize a predisposition 
to disease. 

168. Congenital disease. — The fact that a disease 
exists at birth is not always adequate evidence that 
disease has been inherited. It is possible for certain germ 
diseases to infect the foetus in utero. It is also probable 
that the ova or spermatozoa may under certain conditions 
carry the infection and this infection may be present and 
active during the prenatal life of the animal. 

169. Predisposition to disease. — Many diseases ap- 
pear to " run in families." For this reason we have recog- 
nized the fact that the members of certain families are 
subject to tuberculosis, gout, rheumatism, imbecility, 
insanity or other diseases. In all these cases there exists 
a predisposition on the part of the members of a given 
family to acquire the diseased condition. Through w^eak- 
ness of certain organs or general lack of constitutional 
vigor, the infective germs of many diseases may overcome 
the resistance of the animal organism to disease. This 
predisposition is certainly and often strongly inherited. 
From the standpoint of the practical animal breeder, 
therefore, a predisposition to disease may be quite as 
significant as the actual transmission of the disease. 

170. Immunity. — An interesting correlated fact is 
the probable inheritance of immunity from certain 
diseases. Certain families seem to possess immunity 
from certain diseases, such as smallpox or diphtheria. It 
is not possible at this time to enter into a discussion as 



182 THE BREEDING OF ANIMALS 

to the nature of immunity, but undoubtedly the known 
immunity of certain individuals or families to certain 
diseases may become the basis of important future im- 
provements in the domestic animals. In recent years 
it has been found that certain hogs are immune from hog 
cholera. Experiments have been suggested to deter- 
mine whether or not it would be possible to develop a 
race of swine immune to this dreaded disease. 

It is possible for animals to acquire immunity through 
vaccination of actual infection of the disease itself. Such 
immunity is not transmitted. It is doubtful whether 
there exists any congenital immunity, but investiga- 
tions along this line might be fruitful of results. 



CHAPTER IX 
HEREDITY AND SEX 

The chief function of both plants and animals is to 
live and reproduce. In many wild forms the powers of 
reproduction are little short of marvelous. A single 
plant of purslane may produce a million seeds. Man is 
less productive than most other mammals, but masses of 
population have been known to double in twenty-five 
years. At this rate in 1000 years there would not be 
standing room on the earth for his children. 

The natural increase of plants and animals is not real- 
ized because of unfavorable conditions. The number 
of animals that can exist on a given area is limited. If 
too many are born, some must inevitably die. Others 
are destroyed by enemies, while still others are poisoned 
by substances which accumulate within their own bodies. 

The kinds of reproduction have already been men- 
tioned under the general subject. The simplest form of 
reproduction is by cell division. This method of repro- 
duction is chiefly found in unicellular organisms like the 
amoeba and paramoecium. The most common method 
of reproduction is by eggs. Egg production is almost 
universal among both plants and animals. But the egg 
generally is inert and incapable of development into a 
new individual until it has been fertilized. Herein lies 
the apparent reason for differentiation into male and 
female sexes. 

183 



184 THE BREEDING OF ANIMALS 

171. The significance of conjugation and fertilization. 

— The real purpose of fertilization is not well under- 
stood. Biologists are not yet able to speak with positive 
assurance as to the real character of the actual biological 
phenomena which result from conjugation of the male 
and female germ-cells. Biitschli believed that fertiliza- 
tion was a process of rejuvenation. This idea involves 
the assumption that the union of the germ-cells of two 
weak individuals will result in the production of a strong 
individual. 

Jennings, in a series of very skillful and carefully con- 
trolled experiments with paramoecium, found that after 
conjugation the rate of division was not accelerated but 
was actually slower. Paramoecium which had been 
artificially weakened and their rate of division retarded 
when allowed to conjugate was not in most cases bene- 
fited. Some were apparently benefited, but in all cases 
the rate of division was slower than in cultures in which 
the paramoecium was well nourished. In other words, 
conjugation was of advantage to some and not to others. 
Jennings concluded that conjugation is for the purpose 
of bringing about a recombination of characters. Some 
of them are very beneficial and will persist and multiply, 
others are disadvantageous and these will fail to live and 
reproduce. The combinations most likely to persist 
are heterozygous. 

As Morgan ^ has explained, " The meaning of conjuga- 
tion, and by implication, the meaning of fertilization in 
the higher forms is from this point of view as follows : 
In many forms the race, as a whole, is best maintained 
by adapting itself to a widely varied environment. A 
heterozygous or hybrid constitution makes this possible, 

1 Morgan, "Heredity and Sex," p. 12. 



HEREDITY AND SEX 185 

and is more likely to perpetuate itself in the long run 
than a homozygous race that is from. the nature of the 
case suited to a more limited range of external conditions." 
Whatever may be the real nature and purpose of fertili- 
zation, it is certainly true, as Wilson^ remarks, that '' the 
paternal germ-cell is the carrier of something which 
incites the egg to development, and thus constitutes the 
fertilizing element in the narrower sense." 

172. Secondary sexual characters. — The sexes in 
the higher animals are differentiated, not alone by the 
possession of radically different essential organs of repro- 
duction, but also by the possession of so-called secondary 
sexual characters. The more brilliant plumage of the 
male bird, the horns of the ram, and the greater develop- 
ment of the head and horns of the bull are examples 
of secondary sexual characters. Darwin regarded the 
secondary sexual characters as of great significance in 
sexual selection. As a result of sexual selection he believed 
that '' generally, the most vigorous males, those which 
are best fitted for their places in nature, will leave most 
progeny." ^ 

173. Secondary sexual characters and vigor. — Breed- 
ers of the domestic animals have long regarded the degree 
of development of the secondary sexual characters as 
an index of sexual vigor. Many have held that a male 
with the secondary sexual characters strongly developed 
was not only prepotent in the transmission of purely 
sexual characters but also in other characters which are 
desirable to man. Direct evidence is not available to 
show that because an animal is strongly developed in the 
secondary sexual characters, he is therefore prepotent 

1 Wilson, "The Cell," p. 230 (1911). 

2 Morgan, "Heredity and Sex," p. 101. 



186 THE BREEDING OF ANIMALS 

in the transmission of all characters. Sexual vigor is 
associated with the development of the secondary sexual 
characters, and sexual vigor is a desirable character in 
the domestic animals. The general efficiency of the 
reproductive process is undoubtedly correlated with the 
secondary sexual characters. The breeder, therefore, 
is making no mistake in emphasizing the importance of 
evidences of strong sexuality as indicated by the develop- 
ment of the secondary sexual characters. 

174. Effects of castration and ovariotomy on the 
secondary sexual characters. — There is ample evidence 
of the close correlation existing between the essential 
organs of sexual reproduction and the secondary sexual 
characters. The full development of the secondary 
sexual characters is closely connected with sexual maturity. 
In the Merino breed of sheep, the males are always horned 
while the females are hornless. If the male is castrated 
before the horns begin to develop, the horns fail to grow 
and the wether remains hornless. If the males are 
castrated after the horns have started to develop, the 
horns cease to grow. Marshall, in experiments with 
Herdwick sheep, a breed in which the males are supplied 
with large coiled horns and the females are hornless, found 
that castration at varying ages invariably caused a 
cessation in the growth of the horns of the male. When 
the ovaries of the female were removed, there was no 
apparent tendency toward the growth of horns, although 
small scurs appeared in one spayed ewe that was kept for 
seventeen months after removal of the ovaries. Marshall 
concludes, " The development of horns in the males of 
a breed of sheep in which well-marked secondary sexual 
differentiation occurs (as manifested especially by presence 
or absence of horns) depends upon a stimulus arising in 



HEREDITY AND SEX 187 

the testes, and this stimulus is essential, not merely for the 
initiation of the horn growth, but for its continuance, the 
horns ceasing to grow whenever the testes are removed." 

" The removal of the ovaries from young ewes belong- 
ing to such a breed does not lead to the development of 
definitely male characters, except possibly in an extremely 
minor degree." ^ 

Arkell ^ crossed Merino ewes with a Southdown ram 
(hornless). The sons of this cross had horns. The 
factor for horns in this case must have been present in 
the Merino mother, herself hornless, but the full develop- 
ment of horns cannot take place except the male glands 
are present and functional. 

175. Effect of transplanting sexual glands. — The in- 
vestigations already described seem clearly to point to the 
conclusion that some stimulus to the development of the 
secondary sexual glands exists in the testes and ovaries. 

Steinach transplanted ovarian tissue from a female 
guinea pig to the tissues of a castrated male. The result 
was to cause the rudimentary mammary glands of the 
male greatly to enlarge and the male came to resemble 
the female in certain characters.^ 

A remarkable experiment is described by Goodale ^ in 
which the ovaries of a female Mallard duck were entirely 
removed and the plumage became like that of the male 
Mallard. 

176. Effect of internal secretion. — The secretions 
of various internal organs have a profound influence 
upon the development of the individual. These secre- 

1 Marshall, Proceedings Royal Society (London), ser. B, 85, 
1912. 

2 Arkell, New Hampshire Agr. Exp. Sta., Bui. 160. 

3 Morgan, "Heredity and Sex," 1913, p. 140. 
^ Goodale, Journal Experimental Zoology, 10. 



188 THE BREEDING OF ANIMALS 

tions, called '' hormones," emanate from various glands 
and perhaps from most of the internal organs. If the 
thyroid and parathyroid bodies are removed from the 
body, death follows. The destruction of the pituitary 
glands in man causes the bones of the hands, feet and jaws 
to enlarge (gigantism), causing death. 

It is probable that the milking function in the domes- 
tic animals has some connection with the activities of a 
specific " hormone " which is essential. 

177. Sex-linked characters. — Certain characters are 
so closely related to sex that their transmission is 
influenced by such relation. These characters have 
been called sex-linked or sex-limited characters. They 
are to be distinguished from secondary sexual characters. 

178. Color-blindness. — Men are much more fre- 
quently color-blind than women. Color-blind men do 
not transmit color-blindness directly to sons, but to grand- 
sons through their daughters. The daughters of color- 
blind men are not themselves color-blind, but tend to 
transmit this deficiency to their sons. Color-blindness 
in the daughter could be produced only when the father 
was color-blind and the mother possessed the power to 
transmit color-blindness. Color-blindness is the result of 
some defect in the germ-cell. This factor which is asso- 
ciated with an x chromosome appears twice in the ovum 
and only once in the sperm. A similar condition is found 
in the pomace fly ^ {Drosophila ampelophila) . This form 
has normally red eyes, but this apparently is a unit char- 
acter, sex-linked in transmission. An interesting case 
of sex-linked heredity is found in the Barred Plymouth 
Rock fowl.^ Pure barred fowls when mated produce 

1 Castle, "Heredity and Eugenics," p. 75. 

2 Castle, "Heredity," 1911, p. 170. 



HEREDITY AND SEX 189 

only barred offspring. When the male Barred Rock is 
bred with a non-barred variety, the offspring of both 
sexes are all barred. If the female Barred Rock is mated 
with non-barred breed, the offspring will be about one- 
half barred and the remainder non-barred. The barred 
offspring are always males, while all the females are non- 
barred. The barred character is, therefore, sex-limited. 
The Barred Rock female is heterozygous and the male 
homozygous. The pure Barred Rock breed transmits 
the barred quality because the male is pure in respect to 
the barred character. The same result follows if a cross- 
barred male is mated with barred females. The explana- 
tion of sex-linked inheritance is probably to be found in 
the existence of some plus element in the egg which is 
not found in the sperm. 

179. Controlling the sex of offspring. — In many of 
the domestic animals, the sex of the individual determines 
its peculiar value and usefulness to mankind. If some 
method of breeding could be devised which would result 
in the production of the particular sex desired, it would 
be a great economic gain. That such attempts have 
been made by both ancient and modern breeders is made 
clear from an examination of the literature of the subject 
from the earliest times to the present. Because of the 
more or less general belief among practical breeders in 
the possibility of controlling sex, it seems necessary to 
consider briefly some of the more widely held theories of 
sex control. 

180. Age or vigor of parents. — Two investigators, 
Sadler ^ (1830) in England and Hofaker (1823) in Ger- 
many, collected statistics representing more than 2000 
births. Their statistics showed that when the father is 

1 Carpenter, "Human Physiology," p. 1015. 



190 



THE BREEDING OF ANIMALS 



older the larger number of the offspring are males, and 
when the mother is older the children tend to be females. 
These results have been confirmed by Gohlert, Boulanger 
and Legoyt. Many practical breeders have also cited 
special cases in which the sex offspring seemed to follow 
that of the older parent. Giroude Buzareingues ^ reports 
results from breeding young immature ewes to strong 
mature rams. The proportion of sexes was 80 males 
to 35 females. When young rams were used as sires, 
the proportion of sexes was 53 males and 84 females. 

Summary of Statistics Bearing on Relative Number 

OF Males and Females ^ 









OS ^ 


J Oo 


« r 








Number 




^ O ^ <! 
O i-i to s 




§2pS 






Observer 


OP 


Locality 


«ss« 


«§S^ 


bn H "^ ">J 

•"^ « 32 g 


^ «< 


Remarks 




Births 




si^^ 


Sf^^w 


(B O H H 


oogl 














Fathe 

Prof 

Mal 

F 


is 




Hofaker 


1,996 


Tubingen 


117.8 


92.0 


90.6 


107.5 





Sadler 


2,068 


England 


121.4 


94.8 


86.5 


114.7 


— 


Gohlert 


4,584 


England 


108.0 


93.2 


82.6 


105.3 


— 


Legoyt 


52,311 


Paris 


104.49 


102.14 


97.5 


102.97 


— 


Boulanger 


6,006 


Calais 


109.98 


107.92 


101.63 


107.9 


— 


Noirot 


4,000 


Dijon 


99.7 


— 


116.0 


103.5 


— 


Breslau 


8,084 


Ziirich 


103.9 


103.1 


117.6 


186.6 


— 


Stieda 


100,590 


Alsace- 
















Lorraine 


105.03 


— 


108.39 


106.27 


Contra- 
dictory 


Berner 


267,946 


Sweden 


104.61 


106.23 


107.45 


106.0 


Contra- 
dictory 



^ Quarterly Journal of Agriculture, vol. 1, 1828, p. 63. 
2 Geddes and Thompson, "The Evolution of Sex," p. 



35. 



HEREDITY AND SEX 191 

The differences are not large and the number of observa- 
tions are entirely too few to justify any sweeping conclu- 
sions. Steida ^ and Berner found no relation between 
age and the sex of offspring. The evidence of the in- 
fluence of age on the sex of offspring is too conflicting to 
be conclusive. 

181. Comparative vigor or sexual superiority. — Vari- 
ous authorities have attempted to explain the proportion 
of sexes on the theory that the sex of the offspring will 
correspond to that of the more vigorous or '' superior " 
parent. Darwin, Richarz, Hough and others regarded 
the male as to a certain extent a superior organization, 
and male offspring would result when the reproductive 
functions of the mother were particularly well developed. 
The evidence available is not sufficient to give this hypoth- 
esis any particular importance in practical breeding. 

182. Nutrition and sex. — That the nutritive condition 
of the parents, particularly the mother, at the time of 
fertilization and before has a preponderating influence 
on the sex of offspring has been long believed. Yung 
found that under certain conditions regarded as normal, 
the proportion of sexes in tadpoles was about 57 females 
to 100 males. By feeding the tadpoles beef, fish and 
frog's flesh, the percentage of females enormously in- 
creased, being in one case 92 females to 8 males. An 
interesting case illustrating the connection of nutrition 
and sex is found in bees. The swarm of bees is composed 
of workers (imperfect females), drones (males) and the 
queen (a perfect female). The drones are hatched from 
unfertilized eggs. The queen and workers are developed 
from fertilized eggs, but perform a very different role in 
life. The queen becomes the mother of new generations, 

1 Ihid. 



192 THE BREEDING OF ANIMALS 

while the worker bees are sexually imperfect. It seems 
to be true that the eggs developing into worker bees 
and queens are identical. The one becomes a queen as 
the result of a '' royal " diet, while the worker larvae 
are fed on a " common " diet and develop into the non- 
fertile female. Investigations with wasps by Von Siebold ^ 
and butterflies and moths by Mrs. Treat suggest a real 
connection between nutrition and sex offspring. Schenk 
found that starvation produced fewer males, but later 
the same condition resulted in producing more males. 
Diising reported that among the Swedish nobility the 
proportion of sexes was 98 boys to 100 girls, and in the 
Swedish clergy 108.6 boys to 100 girls. Punnett submits 
evidence that in London more girls are born among the 
poor than the rich. In most of the cases cited there are 
too many other factors involved to justify the conclusion 
that nutrition alone is responsible for the proportion of 
the sexes. 

183. The maturity of the ovum. — The degree of 
development or maturity of the ovum itself at the time 
of fertilization has a controlling influence on sex in the 
opinion of some breeders. If fertilization occurs during 
the early part of the heat, the offspring will be female. 
If the ovum is fertilized later in the heat, the offspring 
will tend to be males. Thus Thury ^ of Geneva says, 
" The sex depends upon the degree of maturity of the 
egg at the moment of fecundation, that which has not 
reached a certain degree of maturity producing the female, 
and, if fecundated when this point of maturity has passed, 
producing a male." These results are not altogether 
consistent with ordinary farm practice or with the experi- 

1 Rolph, W. H., "Biologische Probleme," Leipsig, 1884. 

2 Country Gentleman, 1864, p. 12. 



HEREDITY AND SEX 193 

ments of others. In ordinary breeding operations on the 
range, the bull invariably runs with the cows and breed- 
ing occurs during the first part of the heat. If the sex 
is determined to any extent by the particular stage of 
heat, then in this case the offspring should be largely 
female. But such is not the case, the proportion of the 
sexes is practically equal, subject to seasonal or other 
variations not entirely explainable. Thury's results 
have not been satisfactorily confirmed. Miles ^ recorded 
the proportion of sexes among cattle and sheep on the 
Michigan Agricultural College farm for a period of ten 
years. The results were as follows : Sheep, 102.5 males 
to 100 females. Cattle, 118.4 males to 100 females. All 
the animals were bred during the first part of the heat 
and the offspring should have been more largely female. 
The proportion of the sexes seems to be subject to wide 
variation, and therefore any investigations of this kind 
must necessarily include large numbers of animals and 
the observation be carried over a series of years to make 
the results of any value. 

184. Seasonal variations in proportion of sexes. — 
The proportion of the sexes is subject to wide variations 
apparently due to seasonal influences. Quoting again 
from Miles : ^ 

" In 1864 and 1865 the bull-calves were 2.5 to 1 heifer ; 
in 1866 and 1867 the heifers were considerably in excess ; 
in 1868 and 1869 the heifers were nearly 2 to 1 bulls ; in 

1870 the bulls were decidedly more numerous ; and in 

1871 and 1872 there were more than 2 bulls to 1 heifer. 
In 1872 there were 2 rams to 1 ewe, and the bulls were 
nearly in the same proportion to the heifers, which would 

1 Miles, "Stock Breeding," 1878, p. 265. 

2 Ibid., p. 299. 
o 



194 THE BREEDING OF ANIMALS 

seem to indicate some peculiar influence of the season in 
favor of the males. In 1871, however, the bulls were 
largely in excess of the cow-calves, and there was quite 
as decided a preponderance of females among the sheep." 

185. Sex cannot be controlled by external conditions. 
— The most recent investigations of sex determination 
lead to the belief that sex is predetermined in the germ- 
cell. It is not subject to change through any change in 
the environment, as nutrition or temperature. The 
germ-cell contains a determiner for sex as it contains 
determiners for other characters. 

Castle concludes, ^ ''If, as has been suggested, the deter- 
mination of sex in general depends upon the inheritance 
of a Mendelian factor differentiating the sexes, it is highly 
improbable that the breeder will ever be able to control 
sex. Male and female zygotes should forever continue 
to be produced in approximate equality, and consistent 
inequality of male and female births could result only from 
greater mortality on the part of one sort of zygote than 
of the other." 

The same idea is similarly expounded by Morgan.^ 
" If these observations are confirmed, they show that 
in man, as in so many other animals, an internal mechan- 
ism exists by which sex is determined. It is futile, then, 
to search for environmental changes that might determine 
sex. At best the environment may slightly disturb the 
regular working out of the two possible combinations 
that give male or female. Such disturbances may affect 
the sex ratio but have nothing to do with sex-determina- 
tion. 

1 Castle, "Heredity," 1911, p. 180. 

2 Morgan, "Heredity and Sex," p. 248. 



CHAPTER X 
VARIATION 

No biological fact is more clearly recognized than the 
tendency of all plants and animals to vary. In a broad 
way, individuals resemble their parents. Through hered- 
ity the qualities of the parent are transmitted to the off- 
spring. A horse begets other horses and not pigs. We 
do not gather grapes of thorns nor figs from thistles. 
Thus has come about the old adage " like begets like," 
but this aphorism applies only within certain limits and 
fails to take into account the inexorable law of variation 
by which the offspring is never exactly like the parent. 
It is true that the offspring of a horse will always be a 
horse and not a cow. It is even true that the progeny of 
a trotting horse will be a trotting horse, but the keen 
judge of horses is able to discern slight variations in form, 
color, disposition or ability to perform. 

No two animals are exactly alike. The difference 
may be slight or very marked. From the same sire and 
dam, the offspring may differ widely in character among 
themselves. In a large family of boys, the physical 
characters and mental dispositions of the individual 
members of the family may be very different. It has 
happened in the history of trotting and running horses 
that own brothers have varied widely in their ability 
to win in speed competitions. 

195 



196 THE BREEDING OF ANIMALS 

186. Importance of variability. — The inherent tend- 
ency to vary which exists in all organic beings makes the 
improvement of domestic races possible. Inorganic 
compomids are fixed in composition and physical char- 
acter. Pure gold cannot be improved. The individual 
animal has within its own organic constitution not only 
the capacity for, but a noticeable tendency toward, varia- 
tion from the characters of its ancestors. This fact lies 
at the very foundation of the successful improvement 
of domestic animals. If it were true that the offspring 
was identical in character with the parent, then improve- 
ment would be impossible. 

In developing new varieties, the breeders' efforts 
are sometimes first directed toward encouraging the 
tendency to variation. If the particular form which 
the breeder is endeavoring to improve possesses an unusual 
tendency to vary, then a large number of new characters 
or new combinations of characters will occur. Some of 
these will be desirable, but many will be less desirable 
than in the parent forms. The individuals which possess 
the most useful and valuable characteristics will be pre- 
served by selection. After desirable variations have 
occurred, the next step is to fix these by heredity so that 
they may become racial characteristics and be trans- 
mitted with some degree of regularity from parent to 
offspring. 

187. Morphological variations. — The variations which 
are of interest to the animal-breeder exhibit many differ- 
ent forms. 

Morphological variations are those affecting the form. 
These may be merely differences in size, as in the case 
of two pigs possessing the same characters and the same 
relative development of characters but differing in size. 



VARIATION 197 

Some individuals are dwarfs while others are giants in 
size. This variation in size is due to a difference in the 
number of cells rather than in the size of the cells. The 
increased number of cells found in the larger individuals 
represents excessive cell division, while the abnormally 
small are the result of imperfect and arrested cell division.^ 

The cause of undersized individuals among animals 
cannot always be determined. It is certain, however, 
that insufficient food or food which is deficient in the 
necessary elements of nutrition is a common cause of 
undersized animals. 

It is also true that when females become pregnant 
while still growing and immature, their growth receives 
a sudden check. The arrested development is not so 
much due to the effects of pregnancy as to the strain of 
lactation. The growth of well-fed females is probably 
not to any appreciable extent checked by pregnancy, 
but the physiological requirements for the production 
of milk are severe and the development of immature 
mammalian females is abruptly arrested during the 
period of lactation. 

DiflPerences in size are of relatively less importance than 
morphological differences arising from variation in the 
relative development of the parts of the body. This 
may be illustrated by the variations in meat animals. 
Beef cattle may possess a broad back, well-sprung rib, 
and a thick covering of flesh over all parts, or they may 
lack these highly desirable qualities. 

188. Physiological variations. — Changes in the func- 
tional activities of animals are frequent and important. 
The average domestic cow produces not more than 150 
pounds of butter in a year, but selected herds may produce 

^ Davenport, "Principles of Breeding," p. 27. 



198 THE BREEDING OF ANIMALS^ 

500 pounds of butter in one year. Some individuals 
are very fertile, others may be sterile or markedly deficient 
in this very desirable quality. 

189. Meristic variation. — All plants or animals develop 
in accordance with a certain symmetrical pattern. A 
quadruped has four legs, two ears, two eyes, and two sides 
of similar character. A deviation from the characteristic 
plan or pattern of the species is called a meristic variation. 
Such variations are of very great importance among 
plants, but are of little practical significance to the animal- 
breeder. Examples of meristic variation are to be seen 
in the doubling of flowers, the stooling of grains, and 
the production of four-leaved clovers. Among animals 
the growth of extra fingers and toes, and the development 
of an abnormal number of vertebrae or ribs, are not un- 
common. An interesting example of this type of varia- 
tion is found in the development of extra mammae. 
Supernumerary nipples in mammals are a common form 
of variation among humans. Bruce ^ found fourteen 
cases of extra mammae among 2311 females examined. 
Most male mammals are supplied with rudimentary 
nipples, and curiously there seems a greater amount of 
variation among males than females. The same authority 
quoted above found forty-seven cases of multiple nipples 
among 1645 males examined. In one case a woman ^ 
is reported to have possessed five pairs of nipples. The 
presence of a larger number of mammae than the normal 
has been regarded by some as evidence of greater fertility.^ 
A variation in the opposite direction resulting in the 
development of a smaller number of digits than the normal 

1 Bateson, "Materials for the Study of Variation." 

2 Ibid., p. 183. 

3 Bell, "Multinippled Sheep." 



VARIATION 199 

is to be found in the case of the " mule-footed " hog. In 
this instance, the spht hoof has united into one soUd 
hoof Hke the horse, and this variation is strongly inherited. 
Meristic variations are often transmitted by heredity. 

190. Functional variations. — In our discussion of 
variation up to this point, we have chiefly concerned 
ourselves with such changes as are exhibited in the form 
of animals. We have now to consider those important 
modifications which affect the performance of the indi- 
vidual. An animal may retain the same form as the 
average of the race but be vastly more efficient in the 
performance of some one or more of the physiological 
functions. This type of variation is one of the most 
important to the animal-breeder. The value of many of 
the domestic animals depends entirely upon their func- 
tional development. The chief advantage possessed by 
some domesticated animals over their wild progenitors 
is due to their higher functional efficiency. This is illus- 
trated by the domestic coav, the improved breeds of wool 
sheep, and the trotting horse. Such differences in form 
between the wild and domestic sorts as are present are 
chiefly significant as indicating the correlation which exists 
between function and form. The changed form, if it ex- 
ists, is incidental and the result of functional influence. 

The valuable variation which the breeder has em- 
phasized in his selection has been the ability of the animal 
to produce economically and largely some valued animal 
product. The breeder did not in the beginning consciously 
select variations in form. It is true, however, that the 
efficient performance of animals is to a certain extent 
correlated with the form, and it follows, therefore, that 
we may within certain rather narrow limits rely upon 
the external form as an indication of functional efficiency. 



200 THE BREEDING OF ANIMALS 

191. Examples of functional variation. — In most cases 
the functional variations in the domestic animals which 
have become valuable to man are modifications of natural 
functions possessed by all wild animals living under nat- 
ural conditions. The present stage of development in 
domestic forms is due to artificial selection practiced by 
man. The variations which have been desirable have 
been preserved through selection and a gradual improve- 
ment in functional efficiency has resulted. These varia- 
tions may arise through sudden mutations, but such 
marked changes in function are probably less common 
than similar mutations in form. Variations in the func- 
tional activities of animals are of great economic impor- 
tance to the breeder of domestic animals. It is important 
to know with some degree of definiteness the extent of 
variation in function, as such knowledge will give some 
idea of the probable limits of improvement. The follow- 
ing examples of functional variation will be useful in 
helping to determine the limitations of improvement. 
Such examples may be greatly multiplied by search of 
the literature of the subject. 

192. Variation in fertility of animals. — It is well 
known that there are wide differences among individual 
animals and among races or breeds in their ability to 
produce large numbers of offspring. The quality of 
fertility is one of great practical importance and is readily 
transmitted by heredity. Miles ^ has recorded the case 
of a cow belonging to a French farmer which produced 
nine calves at three births, four at the first, three at the 
second, and two at the third. ^ A Teeswater ewe belonging 
to Edward Eddison produced four lambs in 1772 when 

1 Miles, "Stock Breeding," p. 131. 

2 "British Husbandry," vol. II, p. 438. 



VARIATION 201 

two years old ; " in 1773, five ; in 1774, two ; in 1775, 
five; in 1776, two; and in 1777, two. The first nine 
lambs were lambed within eleven months." ^ The 
Country Gentleman reports the case of a sow that 
produced twenty-three pigs at one birth. The above 
examples are of unusual cases of fertility and are so far 
above the average fertility of the respective races of 
animals that they represent a marked departure from 
the established type. Other things being equal, those 
races of domestic animals which are most fertile are most 
profitable. One of the qualities of economic importance 
which commends certain breeds to the practical farmer 
is the quality of fertility. This is especially true among 
swine and sheep. 

193. Variation in the milking function. — The milk- 
ing function in domesticated animals is of special interest 
for the reason that it is probably the most valuable single 
functional variation in the domestic animals. The im- 
provement of the domestic cow in the direction of greater 
functional efficiency in the production of milk and butter 
has been little short of marvelous. This improvement 
has not only resulted in developing an animal with a 
capacity to produce enormous quantities of milk, but the 
efficiency of the cow in the economic utilization of food 
has been no less noteworthy. The highly improved 
domestic cow is able to utilize the raw products of the 
farm, consisting of grain, hay and grass, and produce 
from these a larger amount of human food than any other 
domestic animal. The high efficiency of the milk cow 
as compared with the beef steer is clearly shown by the 
records kept at the Missouri Experiment Station.^ A 

1 CuUey, "Live Stock," p. 123. 

2 Eckles, ''Dairy Cattle," p. 6. 



202 THE BREEDING OF ANIMALS 

Holstein Friesian cow produced 18,405 pounds of milk 
in one year. This year's production from one cow con- 
tained 2218 pounds of dry matter. At the same station, 
the carcass of a 1250-pound fat steer was analyzed. The 
steer was twenty-one months old and had been fed gen- 
erously from birth. The steer's carcass contained 548 
pounds of dry matter, or a little less than one-fourth the 
amount of dry matter produced by the cow in one year. 
The dry matter recorded for the steer was for the entire 
carcass of the animal, including hide, horns, bones and 
intestines. The actual net weight of the dry matter of 
the edible portion of the fat animal was only 357 pounds. 
In other words, the Holstein Friesian cow produced six 
times as much edible human food in twelve months as 
was produced by the fattening and growing steer in 
twenty-one months. In the case just cited, it is true 
that the cow was far above the average in efficiency while 
the steer was a fair representative of a good average beef 
animal. The example is nevertheless a most excellent il- 
lustration of the very great development and improvement 
of the dairy cow in the direction of desirable variations. 
The foregoing records of the two animals did not include 
the dry matter consumed in the production of milk and 
beef. Such a record which would give the amount of 
dry matter required to produce a pound of dry matter in 
milk as compared with a pound of dry matter in beef 
would be of great interest. Such records have been kept 
at a number of American experiment stations. 

The feed and milk record of Pedro's Ramaposa 181,160 
has been given by Eckles,^ and from this the dry matter 
in feed which is required to produce a pound of dry matter 

^ Eckles, Missouri Experiment Station, Research Bulletin, No. 
2, p. 117. 



VARIATION 203 

in milk can easily be determined. The cow, Pedro's 
Ramaposa, during a period of one year produced 8522.9 
pounds of milk which contained 1317 pounds of dry 
matter. In the production of this quantity of milk she 
consumed in feed 9362 pounds of dry matter. In other 
words, the consumption of 100 pounds of dry matter 
in the feed resulted in the production of 91.12 pounds of 
milk containing 14.06 pounds of dry matter. Stated 
in other terms, the cow here described produced one pound 
of dry matter in the milk for each 7.1 pounds of dry 
matter consumed in the feed. i 

194. Variations among different cows. — The milking 
function is hereditary and is a comparatively well-fixed 
character among the dairy breeds of cattle. It is true, 
however, that there still exist wide variations in the 
productive capacity of cows, even of the same breeding 
as well as those of different ancestry. The Illinois 
Experiment Station ^ in several tests has clearly demon- 
strated the wide differences which may exist between 
individuals.^ Two native cows. Rose, nine years old, 
and Nora, six years old, were fed the same kind of 
a ration for twelve months. The amount fed was de- 
termined by the appetites of the animals. The table 
on the following page gives the essential facts of interest 
in this connection. 

" Reduced to a like feed basis, for every 100 lb. of milk 
given by Nora, Rose gave 139.5 lb., and for every 
100 lb. of butter-fat produced by Nora, Rose produced 
180.7 lb." 

Commenting on this test, Fraser says,^ " As milk is 

1 Fraser, Illinois Experiment Station, Bulletins 51 and 66. 

2 Davenport, "Principles of Breeding," p. 78. 
' Loc. cit. 



204 



THE BREEDING OF ANIMALS 



nearly always valued by the amount of butter-fat which 
it contains, and Rose produced on the same feed basis 
1.807 times as much butter-fat as Nora, the difference in 
yield between the two cows was 252.27 lb. of butter-fat 
or 294.31 lb. of butter per year. This at 16 cents per 
pound, which is the average value of butter before being 
made up, would amount to $47.09 per year. Supposing 
that the cows would yield in this ratio for six years, 
from the age of four to ten, which is a conservative 
estimate, Rose would produce $282.54 worth of butter 
more than Nora on exactly the same kind and quantity 
of feed ; 



Record of the Two Cows for One Year Computed on 

A Like Feed Basis 



Reduced to a like feed basis the 
amount Nora would have pro- 
duced had she eaten the same 
as Rose : 

Total digestible dry matter con- 
sumed in pounds 

Total yield of milk, in pounds . 

Total yield of butter-fat, in 
pounds 

Total yield of butter, in pounds 

Total value of butter at 16 ji per 
pound. . . , 



Rose 



6477.92 
11,329.00 

564.80 
658.90 

$105.43 



Nora 



6477.92 
8121.60 

312.53 
364.62 

$58.34 



Difference 



3207.40 

252.27 

294.28 

$47.09 



" In this comparison Rose was at a disadvantage in 
two ways. She was nine years of age and on the down 
grade of life while Nora was just in her prime. Rose was 
bred November 5, 1899, while Nora was not bred until 



VARIATION 205 

after the experiment closed. Had it not been for these 
two hindrances Rose would doubtless have made even a 
better record than she did. 

" While there is a vast difference in the profit derived 
from the two cows in this experiment, the difference is 
by no means phenomenal, as greater differences than 
here cited may frequently be found among cows in the 
same herd, for the cow Nora, the poorer of the two, was 
in reality an exceptionally good cow, producing 348 lb. 
of butter in a year which is nearly three times the average 
yield (130 lb.) of cows in the United States and almost 
one-half more than the average yield (250 lb.) of profitable 
cows in Illinois. Had Rose been compared with a really 
poor cow, such as may be found in nearly all dairy herds, 
there would have been a much greater difference in profit 
in favor of Rose ; for she gave nearly five times as much 
as a profitable cow for Illinois." 

In the cases of variation mentioned, the individuals 
compared have belonged to different breed-s or have been 
unrelated. It is also true that animals which are from 
parents of the same blood lines may show wide variations. 
In the dairy herd belonging to the University of Missouri, 
there were at one time nineteen daughters of the Jersey 
bull Minette's Pedro. Many of the mothers of these 
cows were from another bull and all were of similar breed- 
ing. The conditions surrounding these cows were alike; 
their dams, grand dams, and great grand dams were all 
similarly bred and every cow of the nineteen was sired 
by Minette's Pedro. These cows should have exhibited 
some uniformity in the development of dairy qualities. 
The table records the annual production of milk and 
butter, and shows rather wide variations in the productive 
capacity of the different cows : 



206 



THE BREEDING OF ANIMALS 



Records of the Daughters of Minette's Pedro ^ 





Number 

Lactation 

Periods 


Average 
Lbs. Milk 


Average 
Lbs. Fat 


Pedro's Ramaposa 


3 


6750 


365.8 


Pedro's Elf ... . 




3 


2225 


109.4 


Pedro's Alphea Elf . 




5 


6151 


309.8 


University May . . 




3 


4723 


227.0 


Columbia Huguita 




5 


6322 


273.1 


Pedro's Daisy Bate . 




2 


3456 


193.7 


Missouri Daizie 




1 


4910 


205.5 


University Daizie . 




4 


7746 


405.6 


University Stella . . 




3 


5336 


273.7 


University Elf . . 




4 


5053 


247.3 


University Belle . 




3 


4960 


223.8 


Pedro's Grace Briggs 




3 


4909 


287.9 


Pedro's Matron 




3 


6582 


355.9 


Miss Missouri .... 




3 


6844 


331.0 


Pedro's Emily Harris 




3 


5271 


238.5 


Pedro's Estella . . . 




2 


8807 


462.1 


Pedro's Alphea Ward 




1 


4728 


267.0 


Pedro's May Hubbard . 




4 


4073 


184.9 


Pedro's Virginia Meredith . 


3 


5776 


320.6 



195. New characters originate in the germ-plasm. — 
In the preceding discussion of the possibiUty of the 
inheritance of acquired characters, we have followed 
closely Weismann's definition of acquired characters. It 
must be admitted, however, that in the discussion of 
this subject by many students of heredity, the use of 
the term has not been confined strictly to Weismann's 
interpretation. Many biologists would include under 
the discussion of this subject all acquired characters, 
regardless of whether they may have originated through 



1 Eekles, Missouri Experiment Station, Research Bulletin, 
No. 2, p. 108. 



VARIATION 207 

environmental influences acting upon the soma-cells or 
from variations directly affecting the germ-plasm itself. 

Many new characters appearing in plants and animals 
cannot be traced to environmental influences acting upon 
the soma-cells. Many characters seem to arise inde- 
pendently of external causes. They undoubtedly have 
their origin in the germ-plasm itself. Such variations 
are fundamentally different from the characters which 
are acquired by the soma-cells as the result of environment, 
use or disuse, disease and mutilations. 

The germ-cell which contains within its own substance 
the materials needed for giving direction to the develop- 
ment of the new individual is the result of the union of 
two other germ-cells from individuals which may repre- 
sent widely different characters. It is impossible that 
the new individual arising from such a germ-cell shall 
possess characters identical with either parent. The 
offspring represents a certain amount of variation which 
had its origin in the germ-cell itself. 

The mechanism of reproduction, including the matura- 
tion and reduction of the germ-cells and the union of the 
chromosomes, provides ample opportunity for new com- 
binations of characters which may profoundly change 
the whole physiological history of the offspring. 

196. Mutilations. — Many examples of mutilations 
and their supposed transmission from parent to offspring 
have given to advocates of the belief in the transmission 
of acquired characters many of their most interesting 
examples. Various investigators have cut off the tails 
of mice for many generations with a view to investigating 
the result of such mutilation upon its transmissibility. 
Cope, Mantegazza and Rosenthal cut off the tails of mice 
for eleven generations. Bos for fifteen, and Weismann 



208 THE BREEDING OF ANIMALS 

for nineteen generations, but in no single case was there 
the sHghtest evidence that this form of mutilation was 
transmitted. 

The tails of sheep have been cut off for many hundred 
years by shepherds, but tails reappear regularly with the 
normal number of vertebrse and without diminution in 
length. 

A large number of examples have been given of cats 
whose tails have been removed and who have later trans- 
mitted to their offspring a tendency to short tails. In 
the Eiffel, the peasants shorten the tails of cats. It is 
reported by Tietz that cats with defective tails are common 
in this region. Many similar examples are reported. In 
this and most other examples of the inheritance of acquired 
characters, there is no evidence that the artificial shorten- 
ing of the tails is the direct cause of the atrophied tails 
observed in the kittens. Such defective tails are not 
uncommon in races of cats with normal tails. It must 
also be remembered that there are tailless breeds of cats 
such as the Manx and Japanese breeds, and the admixture 
of such breeds might be sufficient to explain the observed 
variations. 

The cattlemen of the Nile Valley have for an unknown 
period of time caused the horns of cattle to grow in curi- 
ous spiral forms, but there is no evidence that such 
deformities are transmitted to the offspring.^ 

197. The Brown-Sequard experiments,^ — The most 
frequently quoted and credible scientific experiment 
conducted for the purpose of causing somatic modifica- 
tions and observing their transmission from parent to 

1 Hartman, "Die Haussaugethiere der Wildlander," Ann. 
Landwirthsch., Berlin, 1864, p. 28. 

2 Romanes, "Darwin and after Darwin," vol. II, chap. IV. 



VARIATION 209 

offspring are the famous Brown-Sequard experiments 
with guinea pigs. From 1869 to 1891, Brown-Sequard 
cut the sciatic nerve of the leg or the spinal cord in the 
dorsal region, causing an abnormal nervous condition 
resembling the symptoms of epilepsy. These animals when 
allowed to breed produced offspring, many of which were 
epileptic like the parents. Similar results were later 
secured by Westphal, Dupuy, Obersteiner and Romanes. 
This interesting investigation has been promptly accepted 
by the special advocates of the transmission of acquired 
characters as fulfilling the oft repeated demand for direct 
evidence of the inheritance of somatic modifications. 

In discussing the results it must not be forgotten that 
the mutilation was never transmitted, but only the epilep- 
tic state resulting from the mutilation. The results from 
this type of mutilation were very diverse. According to 
Romanes, the epileptic condition was rarely transmitted. 
Brown-Sequard admitted that certain particular results 
were exhibited in only one or two per cent of cases. If 
this mutilation had actually influenced the germ-plasm 
in such a way as to add to its fundamental constitution 
the determiners essential for the development of the new 
characters, then surely we might expect a larger part of 
the offspring to be affected with the acquired character. 

Max Sommer in 1900 repeated the Brown-Sequard 
experiments, but failed to confirm the conclusion that 
this experiment had proven the existence of acquired 
characters. " As regards the hereditary transmission of 
epilepsy in guinea pigs," says Sommer, "or of other 
accidentally acquired pathological symptoms — e.g. de- 
fects in the toes — we have not been able to confirm 
the experiments of Brown-Sequard and Obersteiner; 
and we do not think that these can any longer serve as 



210 THE BREEDING OF ANIMALS 

a support to the doctrine of the inheritance of acquired 
characters." ^ 

198. Causes of variation. — The nature of variation 
is still obscure. The fundamental causes are not easily 
determined. " Our ignorance of the laws of variation 
is profound/' says Dgj'win. 

The results of the investigations in cytology have given 
a more reasonable basis for understanding the subject 
of variation, but it has not yet given us a wholly satis- 
factory knowledge of the causes of variation. Bateson 
holds that we are yet far from a satisfactory explanation 
of the real nature of variation. He has concluded that 
'' Inquiry into the causes of variation is, in my judgment, 
premature." We are, however, able to recognize and 
classify certain apparent causes of variation. Such clas- 
sification recognizes causes of variation as external and 
internal. 

Davenport ^ has further classified the internal causes 
of variation as: ''1. Internal influences affecting pri- 
marily the individual, and 2. internal influences affecting 
the race as a whole." 

199. Cell division a cause of variation. — Every animal 
is the product of the union of the germ substance of two 
other animals. The union of the germ-cells is a union 
of the characters of the parents. This combination of 
the germinal matter of the two parents results in a rear- 
rangement of some of the characters, and these may vary 
materially from the original characters of the parents. 
Weismann calls this mixing of the germ-plasm amphimixis. 
He is of the opinion that sexual reproduction by cell union 
and cell division is nature's plan for increasing variation. 

1 Thomson, " Heredity," pp. 230-236. 

- Davenport, "Principles of Breeding," p. 155. 



VARIATION 211 

New characters may arise or old ones be lost through 
accidents to the germ substance during the processes of 
cell division incident to reproduction and growth. It is 
conceivable that a chromosome bearing within its ma- 
terial substance a character or set of characters may be 
lost or destroyed at some stage of the complicated pro- 
cesses which eventually result in the formation of a new 
germ-cell. If such a thing occurs, it must influence 
greatly the ultimate characters of the individual. It is 
also apparent that a fundamental change in the germinal 
material may influence not alone the resulting individual 
but the race or breed. Sudden marked variations may 
and do often occur, and these may become the beginnings 
of new races. These sudden variations are called muta- 
tions by De Vries, and the mutation theory of evolution 
is regarded as one of the most important advances since 
Darwin. A fuller discussion of mutations will be found 
on another page. 

It is difficult to differentiate between those variations 
which are merely the result of the action of environment 
on the soma- or body-cells and those variations which 
are the result of a fundamental change in the constitu- 
tion of the germ substance. The former are generally 
temporary and affect only the individual, but do not 
influence the germ sufficiently to cause the same varia- 
tion to appear in the offspring. The highly improved 
types of domestic swine if permitted to run wild in the 
woods lose their rounded full-fleshed form and assume 
much the appearance of the unimproved " razor-back.'* 
Their appearance is so changed by this treatment that 
the most skillful judge of swine would be greatly deceived. 
The ^' razor-back," on the other hand, has subsisted for 
generations upon the mast of the forest. This has in- 



212 THE BREEDING OF ANIMALS 

volved much exercise and the ability to Hve on a scant 
supply of food at certain seasons. These conditions have 
resulted in changing the form of the body. The neck 
and jaws are larger and well muscled. The back is sharp, 
legs longer and ribs flatter than in the improved forms. 
If the young pigs of these unimproved swine are placed 
under conditions where they are supplied with an abun- 
dance of nutritious food, they approach somewhat the well- 
rounded form of the improved type. In each of these 
cases the environment has resulted in causing a distinct 
variation from the parent form. This variation can be 
easily observed, it can be measured. But whether this 
environment has influenced in any way or how much it 
has influenced the elemental carriers of heredity in the 
germ, it is impossible to do more than conjecture. It 
cannot be accurately measured. Biologists are generally 
agreed that in a case of this kind the germ is not funda- 
mentally changed. 

200. Influence of use and disuse in causing modifica- 
tions. — The constant use of an organ in the performance 
of work will modify the organ in accordance with the work 
performed. Any organ of the body that is not used may 
atrophy. Changes resulting from excessive use of the 
various parts of the body may be so extensive as to appear 
almost as new characters. If modifications resulting 
from food, climate or mutilations are transmitted, the 
changes resulting from the constant use of an organ should 
be transmitted with equal or greater force. 

Lamarck's theory of evolution was largely based upon 
the supposed adaptation of the various organs of the 
body to their environment, and that such adaptations 
were readily transmitted. Thus the giraffe, forced by 
conditions to feed upon the leaves of trees, gradually 



VARIATION 213 

extended his neck, which became longer, and this increase 
in length was transmitted from generation to generation. 
Wading birds, feeding in the shallow water along the shore, 
gradually waded deeper and deeper into the water. 
Their legs became longer, and the additional length gained 
by each generation was transmitted. The long tongue 
of the ant-eater, of woodpeckers, and humming birds, 
was developed . in a similar manner. The rudimentary 
eyes of subterranean animals and fish in caves is another 
supposed example of the loss of an organ through disuse. 

Among domestic animals, there are numerous examples 
of a high degree of development of organs through con- 
tinued exercise. The milking function in the dairy cow 
can undoubtedly be greatly improved in any individual 
by skillful exercise and use. The training of running and 
trotting horses has resulted in very greatly increasing 
the ability of an animal in those particular types of speed. 
Are these modifications, the result of use or disuse, trans- 
mitted by heredity? Such inheritance would be of the 
very greatest importance to the breeder of domestic 
animals. In answer to this question no direct proof has 
been offered that characters acquired by exercise or lost 
by disuse are actually transmitted by heredity. 

201. Importance of causes of variation to the breeder 
of domestic animals. — While the researches of biologists 
have led them to believe that the germ-plasm is very 
stable and its character not easily changed by the environ- 
ment of the body, it is nevertheless true that breeders of 
the domestic animals have long believed that the amount 
and kind of food, climate and training which animals 
receive has an influence not only upon the individuals 
benefiting by or suffering from such environment, but 
likewise may have a profound influence upon their pos- 



214 THE BREEDING OF ANIMALS 

terity. The breeder of beef cattle believes that the off- 
spring of parents which are kept in good or even in fat 
condition are more apt to possess a tendency to fatten 
readily than the offspring of parents kept in very thin 
condition. The breeder of trotting horses prefers to use 
in his stud a stallion that has a record and mares that 
have benefited from severe training. 

In this case the biologist ivS, probably in the main cor- 
rect in his conclusions from the standpoint of inheritance. 
But it is also true that the breeder of beef cattle is right 
in maintaining his beef animals on a high plane of nutri- 
tion, not because this will materially affect the germ-plasm, 
but because such treatment gives the breeder an accurate 
measure of the beef-producing characters of his breeding 
animals. How can the breeder know that a particular 
bull or cow possesses the ability to lay on fat rapidly 
unless he actually tests the animal? The breeder of 
trotting horses likewise cannot judge accurately from an 
external examination of a horse how fast he can trot. He 
must be trained and his full speed developed. 

Such treatment on the part of the breeder is not for 
the purpose of changing the hereditary capacities of an 
animal, but for the purpose of aiding selection. Animals 
so treated that do not come up to the standard set by the 
breeder are eliminated. The desirable animals are pre- 
served and encouraged to reproduce. 

202. Germinal variations. — The term variation has 
suffered from careless use, and such use has led to some 
confusion of ideas. Differences appearing in the offspring 
may be due to variations in the germ, or they may be due 
to the influence of environment. What the animal 
actually is depends upon the constitution of the germ. 
The offspring may be exactly like the parent in the con- 



VARIATION 215 

stitution of the germ substance from which each has 
been developed, but they may appear to be different. 
Such differences may be due to a change in the environ- 
ment which, acting upon the organism, may have modified 
the apparent character of the individual. Such changes 
are not variations in the true sense, but rather modifica- 
tions. It is not always possible to distinguish readily 
between changes which are merely modifications and 
variations which are due to fundamental changes in the 
germ. To the practical breeder, it is in the highest 
degree important that this distinction between mere 
modifications due to environment and germinal varia- 
tions due to a change in the constitution of the germinal 
substance be clearly recognized. The latter variations 
are strongly transmitted by heredity; the former are 
not transmissible. Domestic animals kept under the 
same conditions often exhibit wide variations, and these 
are often germinal and consequently inherited. Those 
variations or, more properly, modifications which appear 
in individuals and are the result of environment are of 
little significance to the breeder. If the breeder of speed 
horses confined his selection solely to those horses that 
had been trained, he might not secure the sum total of 
those characters in the fundamental constitution of the 
animal which represent the highest capacity for speed. 
It is true that among horses of similar ancestry the train- 
ing and development is the most accurate index of the 
capacities which they have inherited. But a horse 
that has not been trained and hence modified by environ- 
ment may actually possess through inheritance a greater 
capacity for speed. The latter horse may show less 
speed than the horse that has been carefully developed, 
but he will be a better breeder. Let us assume for example 



216 THE BREEDING OF ANIMALS 

that we have two horses under consideration, of the same 
ancestry. One horse has through germinal variation 
been endowed with an abihty to trot or run at a certain 
speed without training. The other horse cannot attain 
the same speed except as the result of long and careful 
training. They have attained the same rate of speed, 
but one has acquired this speed through the influence 
of environment and this increased speed becomes, there- 
fore, a mere modification. The other horse owes his 
ability to go fast to a variation in the fundamental con- 
stitution of the germ substance. The latter horse will 
be the better breeder because germinal variations are 
transmitted, and modifications which result from the 
influence of environment are apparently not transmitted. 



CHAPTER XI 
IN-BREEDING 

The breeder of domestic animals is frequently confronted 
with the problem of in-breeding. If in-breeding is not 
followed by injury, it would often be a convenient method 
of improvement. The value of a proven and tested sire 
is so great that if he could be safely mated with his own 
offspring it would be of great economic advantage to 
the breeder. If, on the other hand, positive advantages 
follow the mating of closely related animals, the breeder 
should know what these advantages are and how and when 
they may be most certainly realized. 

203. Definitions. — In-breeding has been variously 
designated as close-breeding, consanguineous breeding, 
in-and-in-breeding, inter-breeding and incestuous breed- 
ing. The term in-breeding is used to indicate the mating 
of animals which are near of kin or closely related. The 
degree of relationship which it is proper to designate 
as in-breeding is a matter of some disagreement. Stone- 
henge, for example, has defined in-breeding as '' The 
pairing of relations within the degree of second cousins, 
twice or more in succession." Randall would restrict 
the application of the term to " animals of precisely the 
same blood as own brother and sister." 

It would be very desirable if the term " in-breeding " 
could be limited in its application as suggested by Mor- 

217 



218 THE BREEDING OF ANIMALS 

gan} " For species with separate sexes the term ' in- 
breeding ' is used to express either the union between 
brothers and sisters or between offspring and parent, in 
one or more generations." Unfortunately the Hterature 
on the subject of in-breeding has not placed such narrow 
limitations on the term. 

It must be recognized that there are different degrees 
of in-breeding. Animals may be closely in-bred as, for 
example, results from the mating of parent and offspring, 
or brother and sister. The union of more distant rela- 
tionships, as third or fourth cousins, would not be expected 
to show the same good or bad results in the offspring as 
the more closely related parents. In the literature of 
the subject, the discussions generally have reference to 
the most intensive forms of close-breeding. The results, 
good or bad, therefore, are those which may be expected 
to follow the most intensive in-breeding. After all, the 
real question of importance for the practical breeder to 
answer is not whether any form of in-breeding should 
be practiced, but to what extent it may be practiced and 
its known advantages become realized. In a sense, prac- 
tically every registered improved breed to-day is the 
result of a certain amount of in-breeding. David Starr 
Jordan has calculated that if no in-breeding of any degree 
had taken place in the human race, each person born 
in the thirtieth generation from William the Conqueror 
would have had 8,598,094,592 living ancestors at the 
time when the Conqueror was alive. 

204. Advantages claimed for in-breeding. — The mat- 
ing of animals having the same parentage, has resulted 
in certain definite advantages to the race or breed. These 
results are as easily demonstrable as are the results from 

1 Morgan, "Experimental Zoology," 1907, p. 186. 



IN-BREEDING 219 

any other system or method of breeding. The particular 
beneficial result most commonly claimed is that in-breed- 
ing is the quickest method of fixing and perpetuating a 
desirable character. Closely related animals are most 
likely to possess the character sought, and mating animals 
having the qualities which the breeder particularly desires 
to perpetuate in the breed is the most natural method 
of accomplishing his purpose. In-breeding tends to in- 
tensify the good qualities which the breeder is striving 
to make dominant. It does not cause new and desirable 
characters to appear, but is merely a method of making 
the greatest possible use of such characters. 

Thus in-bred animals are strongly prepotent. They 
possess to an unusual degree the power of fixing their 
qualities upon their offspring. This is manifestly the 
most important characteristic in a highly improved breed- 
ing animal. Next to the possession of the highly improved 
characters which make the domestic animals useful to 
man, their ability to transmit those qualities is most 
important. In-breeding is one certain means of develop- 
ing the prepotency of animals. 

It is a fundamental principle of breeding that the 
smaller the number of qualities selected for improvement 
by the breeder, the more rapid and certain will be his 
progress in the improvement of the breed. In- 
breeding tends to reduce the number of characters, sim- 
plify the breeding operations, and thus makes more 
certain the continued reappearance of the valuable 
characters in succeeding generations. 

205. Bad results from in-breeding. — In recounting 
the well-known benefits which follow intelligent in-breed- 
ing, it is not intended to convey the impression that 
in-breeding results only in success. The biological pro- 



220 THE BREEDING OF ANIMALS 

cesses which result in simphfying the germ-plasm and 
intensifying the powers of transmission act impartially 
on all characters alike, bad as well as good. Lurking 
tendencies to evil may become strengthened along with 
the good, and thus be more strongly transmitted than 
before. 

Such a result cannot always be foreseen and hence 
when breeding closely related animals, there is always 
the risk that we will produce offspring which are not only 
more prepotent in respect to the good qualities we are 
seeking to develop and perpetuate, but we may at the 
same time bring about the same result in connection with 
the bad qualities. 

But aside from the bad results following in-breeding 
which may be ascribed to the simplifying of the germ- 
plasm and the intensifying of the tendencies to evil, it 
has long been held by many eminent biologists and by 
practical breeders that certain definite evil results always 
follow long-continued in-breeding. The most important 
of these necessary evils are loss of vigor, decreased fer- 
tility and diminished size. 

206. Decreased fertility and vigor from in-breeding. — 
Many breeders believe that continuous in-breeding results 
in a loss of fertility. It is admitted that most other 
qualities may be advantageously improved by close- 
breeding, but that the quality of fertility is an exception. 
This belief is firmly implanted in the minds of the greater 
number of breeders and of many biologists. The basis 
for such a belief is found in the results of certain specific 
investigations and the general experience of breeders. 
Fertility is a character of prime importance in the domestic 
animals. This character is undoubtedly subject to the 
same general laws of transmission as are all other hered- 



IN-BREEDING 221 

itary qualities. We have seen how in-breeding may be 
used to intensify and fix the other desirable characters 
of a breed, and incidentally greatly increase their pre- 
potency. If an animal is possessed of the quality of 
fertility to an unusual degree, why may not in-breeding 
be employed to increase fertility as well as to improve 
the qualities of speed in horses or of early maturity 
in meat-producing animals ? Let us answer the question 
by an examination of the available data. Is in-breeding 
yer se specifically injurious to the fertility of plants and 
animals? If in-breeding is injurious at all, how serious 
is the injury and how far can the breeder take advantage 
of the known good results without sacrificing the impor- 
tant quality of fertility ? The data available for answer- 
ing these questions are to be found in the practical experi- 
ence of breeders and the results from carefully planned 
experiments where all other factors have been eliminated 
excepting only the factor of in-breeding. 

207. Darwin's researches. — The greatest single con- 
tribution to the subject of in-breeding was made by Dar- 
win. Recognizing the advantages of close in-breeding 
in fixing desirable characters and admitting that these 
advantages may outweigh possible injur^^ he brings 
forward an array of examples of the injurious effects of 
in-breeding which are convincing. His conclusions are 
best stated in his own words : 

^ " That any evil directly follows from the closest 
inter-breeding has been denied by many persons ; but 
rarely by any practical breeder; and never, as far as I 
know, by one who has largely bred animals which prop- 
agate their kind quickly. Many physiologists attribute 

^ Darwin, "Animals and Plants under Domestication," vol. 
II, p. 94. 



222 THE BREEDING OF ANIMALS 

the evil exclusively to the combination and consequent 
increase of morbid tendencies common to both parents; 
and that this is an active source of mischief there can be 
no doubt. It is unfortunately too notorious that men 
and various domestic animals endowed with a wretched 
constitution, and with a strong hereditary disposition 
to disease, if not actually ill, are fully capable of procre- 
ating their kind. Close inter-breeding, on the other hand, 
often induces sterility ; and this indicates something quite 
distinct from the augmentation of morbid tendencies 
common to both parents. The evidence immediately 
to be given convinces me that it is a great law of nature, 
that all organic beings profit from an occasional cross 
with individuals not closely related to them in blood ; 
and that, on the other hand, long-continued close inter- 
breeding is injurious." 

Darwin's conclusions are based upon a very large 
number of observations. Experienced breeders who are 
accurate observers, such as Sir J. Sebright,^ Andrew 
Knight and Herman von Nathusius, all agree as to the 
certain injury which always follows long-continued in- 
breeding. 

Darwin's investigations led him to believe that while 
many species of plants and animals are hermaphroditic 
and hence self-fertilizing, and these might be presumed 
perpetually to fertilize themselves, yet he failed to find 
a single species in which nature had provided structures 
which insured self-fertilization. On the other hand, he 
found innumerable instances in which nature had pro- 
vided special structures for the sole apparent purpose of 
insuring cross-fertilization and thus preventing perpetual 
in-breeding. 

1 Sebright, "The Art of Improving the Breed," 1809. 



IN-BREEDING 223 

208. In-breeding cattle. — BakewelFs ^ (1725-1795) 
phenomenal success in the rapid improvement of horses, 
cattle and sheep was possible only because he utilized 
to the fullest extent the method of mating animals of 
the closest possible relationship, not because they were 
closely related but because they possessed the particular 
qualities desired. By in-breeding he was able to " sim- 
plify " the germ-plasm and bring about a homozygous 
condition of these particular characters. The available 
breeding records of the activities of Robert and Charles 
Colling, Thomas Bates and the Booths are eloquent in 
their testimony of the fact that great progress was achieved 
from intelligent in-breeding. 

The Shorthorn bull, Duke of Airdrie (12,730),2 traces 
through five or six generations to but six animals famous 
in the early history of the Shorthorn breed. The six 
animals all trace back through five or six generations to 
one bull Favourite, himself the son of half-brother and 
sister. Says Darwin,^ " But the Shorthorns offer the 
most striking case of close inter-breeding ; for instance, 
the famous bull Favourite (who was himself the offspring 
of a half-brother and sister from Foljambe) was matched 
with his own daughter, granddaughter, and great-grand- 
daughter; so that the produce of this last union, or the 
great-great-granddaughter, had 15-16ths, or 93.75 per 
cent of the blood of Favourite in her veins. This cow 
was matched with the bull Wellington, having 62.5 per 
cent of Favourite blood in his veins, and produced Cla- 
rissa ; Clarissa was matched with the bull Lancaster, hav- 

lYouatt, ''Cattle," p. 199. 

2 A valuable discussion of in-breeding among early breeders 
is to be found in Miles' "Stock Breeding," pp. 137-189. Also 
Huth, "The Marriage of Near Kin," pp. 242-292. 

^ Darwin, "Animals and Plants under Domestication," p. 96. 



224 THE BREEDING OF ANIMALS 

ing 68.75 of the same blood, and she yielded valuable 
offspring. Nevertheless Collings, who reared these ani- 
mals, and was a strong advocate for close-breeding, once 
crossed his stock with a Galloway, and the cows from 
this cross realized the highest prices. Bates's herd was 
esteemed the most celebrated in the world. For thirteen 
years he bred most closely in-and-in ; but during the 
next seventeen years, though he had the most exalted 
notion of the value of his own stock, he thrice infused 
fresh blood into his herd : it is said that he did this, not 
to improve the form of his animals, but on account of 
their lessened fertility." 

The opinion of a great breeder who has practiced 
very close in-breeding for eighty years and who has also 
been noted for the general success of his breeding opera- 
tions and the high quality of his cattle, so much so as to 
have been called one of the founders of the breed, is of 
great interest in this connection. Such a breeder was 
Price of England. He says,^ " My herd of cattle has, 
therefore, been bred in-and-in, as it is termed, for upward 
of eighty years, and by far the greater part of it in a direct 
line, on both sides, from one cow now in calf for the twen- 
tieth time. I have bred three calves from her, by two 
of her sons, one of which is now the largest cow I have, 
possessing also the best form and constitution ; the other 
two were bulls, and proved of great value, thus showing 
indisputably that it is not requisite to mix the blood of 
the different kinds of the same race of animals, in order 
to keep them from degenerating." 

209. The Chillingham cattle. — The wild white cattle 
of Great Britain are believed to be the only living pure 
descendants of the original wild cattle of the British Is- 

1 Farmers' Magazine, 1841, vol. XIV, p. 50. 



IN-BREEDING 225 

lands. These cattle have been kept pure in various 
private parks of Great Britain and have for many hundred 
years been subjected to conditions which compelled 
extensive in-breeding. These cattle have not perished, 
they are not weak in constitution and are not decreasing 
in size. This example is often quoted as an argument 
in favor of in-breeding. Darwin's critical analysis of 
this classic example leaves us still in doubt as to its value 
as a demonstration of the beneficial results which may be 
expected to follow long-continued in-breeding. 

^ " The half-wild cattle," says Darwin, " which have 
been kept in British parks probably for 400 or 500 years, 
or even for a longer period, have been advanced by Culley 
and others as a case of long-continued inter-breeding within 
the limits of the same herd without any consequent injury. 
With respect to the cattle at Chillingham, the late Lord 
Tankerville owned that they were bad breeders. The 
agent, Mr. Hardy, estimates (in a letter to me dated 
May, 1861) that in the herd of about 50 the average num- 
ber annually slaughtered, killed by fighting and dying, 
is about 10, or one in five. As the herd is kept up to 
nearly the same average number, the annual rate of in- 
crease must be likewise about one in five. The bulls, 
I may add, engage in furious battles, of which battles 
the present Lord Tankerville has given me a graphic 
description, so that there will always be rigorous selec- 
tion of the most vigorous males. I procured in 1855 
from Mr. D. Gardner, agent to the Duke of Hamilton, 
the following account of the wild cattle kept in the Duke's 
park in Lanarkshire, which is about 200 acres in extent. 
The number of cattle varies from 65 to 80 ; and the num- 
ber annually killed (I presume by all causes) is from 8 

1 Darwin, "Animals and Plants under Domestication," p. 97. 
Q 



226 THE BREEDING OF ANIMALS 

to 10; so that the annual rate of increase can hardly be 
more than one in six. Now in South America, where 
the herds are half-wild, and therefore offer a nearly fair 
standard of comparison, according to Azara the natural 
increase of cattle on an estancia is from one-third to one- 
fourth of the total number, or one in between three and 
four, and this no doubt applies exclusively to adult ani- 
mals fit for consumption. Hence the half-wild British 
cattle which have long been inter-bred within the limits 
of the same herd are relatively far less fertile. Although 
in an unenclosed country like Paraguay there must be 
some crossing between the different herds, yet even there 
the inhabitants believe that the occasional introduction 
of animals from distant localities is necessary to prevent 
' degeneration in size and diminution in fertility.' The 
decrease in size from ancient times in the Chillingham 
and Hamilton cattle must have been prodigious, for 
Professor Rutimeyer has shown that they are almost 
certainly descended from the gigantic bos primigenius. 
No doubt this decrease in size may be largely attributed 
to less favorable conditions of life ; yet animals roaming 
over large parks, and fed during severe winters, can hardly 
be considered as placed under very unfavorable condi- 
tions." 

210. Deer in parks. — In many English parks fallow 
deer have been kept for many decades, and in-breeding 
must often result. An investigation by Darwin dis- 
closed the fact that the managers of such parks found it 
necessary to introduce new blood to improve the size, 
constitution, vigor and prevent the taint of " rick back," 
which follows too close breeding. 

211. In-breeding among pigs. — The evil results from 
in-breeding are naturally more quickly apparent among 



IN-BREEDING 227 

animals which produce large numbers of young at a birth 
and have a comparatively short period of gestation. 
Domestic swine fulfill these conditions admirably and 
are therefore most valuable material for breeding experi- 
ments. 

^ '' Mr. J. Wright, well known as a breeder, crossed 
the same boar with the daughter, granddaughter, and 
great-granddaughter, and so on for seven generations. 
The result was, that in many instances the offspring failed 
to breed; in others they produced few that lived; and 
of the latter many were idiotic, without sense, even to 
suck, and when attempting to move could not walk 
straight. Now it deserves especial notice, that the two 
last sows produced by this long course of inter-breeding 
were sent to other boars, and they bore several litters 
of healthy pigs. The best sow in external appearance 
produced during the whole seven generations was one 
in the last stage of descent; but the litter consisted of 
this one sow. She would not breed to her sire, yet bred 
at the first trial to a stranger in blood. So that, in Mr. 
Wright's case, long-continued and extremely close inter- 
breeding did not affect the external form or merit of the 
young; but with many of them the general constitution 
and mental powers, and especially the reproductive func- 
tions, were seriously affected." 

Nathusius reports that as a result of closely in-breed- 
ing Yorkshire swine for three generations the offspring 
were weak in constitution and their fertility was impaired. 

212. In-breeding sheep. — The American Merino sheep 
is a remarkable example of what intelligent breeding and 

1 Darwin, "Animals and Plants under Domestication," p. 
101. 

Also Journal of Royal Agricultural Society, 1846, vol. 7, p. 205. 



228 THE BREEDING OF ANIMALS 

selection can accomplish in the improvement of the 
domestic animals. The first importation of Spanish 
Merino sheep to America was made in 1815. The aver- 
age weight of fleece of these sheep at that time was 
three or four pounds a head. This average was in- 
creased by- American breeders until, in 1880, the average 
fleece from selected flocks was fifteen pounds a head, and 
single individuals were produced which sheared as high 
as thirty-five pounds. Plumb ^ reports that the heaviest 
fleece on record weighed 44 pounds and 3 ounces and was 
taken from a two-year-old ram at the public shearing 
of the Vermont Sheep Shearing Association. But the 
finest specimens of the American Merino breed were the 
result of in-breeding. '' Mr. Atwood bred his entire flock 
from one ewe, — and thus, after being drawn beyond all 
doubt from an unmixed Spanish Cabana, they have 
been bred in-and-in, in the United States, for upward 
of sixty years." ^ " The ram Gold Drop for which Mr. 
Hammond refused twenty-five thousand dollars," ^ was 
closely in-bred. 

213. In-breeding dogs. — Many examples of in-breed- 
ing among dogs are mentioned in the literature of breed- 
ing, but unfortunately the records of these cases are very 
incomplete and many are of doubtful scientific value. 
The author has had an opportunity to examine somewhat 
carefully the results of long-continued in-breeding among 
fox terriers. Arthur Rhys, the herdsman at the University 
of Missouri, has practiced very close in-breeding of fox 
terriers for nine generations. Daughter No. 1, from 
wholly unrelated parents, was bred back to Designer, her 

^ Plumb, "Types and Breeds of Farm Animals," p. 349. 

2 Randall, "Practical Shepherd." 

3 Miles, "Stock Breeding," p. 150. 







f » .*-^» 




Plate XIV. — Upper. Close in-breeding of fox terrier. "Dis- 
patcher" at age nine months ; ninth generation of intense in-breeding. 
Lower. "Designer 2d" at age four months; eighth generation of in- 
tense in-breeding. 



IN-BREEDING • 229 

own sire, producing two litters of six and seven each. 
Female No. 2, a daughter of No. 1, was bred to Designer, 
her own sire, who was also her grandsire. She produced 
a litter of eight. Female No. 3, a daughter of No. 2, 
was bred again to Designer, her own sire, who was also 
her grandsire and great-grandsire. Female No. 4 was 
again bred to Designer, her own sire, who was also 
her grandsire, great-grandsire and great-great-grandsire. 
She produced a litter of eight. Thus in turn Females 
Nos. 5, 6, 7 and 8 were bred to their own sire, Designer. 
Female No. 8, resulting from this long-continued in-breed- 
ing, was bred to her own son, and from the litter result- 
ing a brother and sister were selected and in-bred. Mr. 
Rhys states that, " I see no evidence of decrease in size 
of bone, in constitution or in fertility as a result of my 
experience in in-breeding fox terriers." The only pecul- 
iarity which has been observed in the later generations 
as compared with the original animals is a slight lack of 
courage or " nerve " in the later animals. A normal fox 
terrier never flinches in the face of sudden danger. 

The illustration, Plate XIV, lower, represents Designer 
II, at four months old, one of the seven dogs in the 
eighth generation of continuous in-breeding. Every litter 
for eight generations was sired by Designer I. The illus- 
tration, Plate XIV, upper, pictures the dog Dispatcher of 
the ninth generation, son of own brother and sister. 

214. Cornevin's ^ experiments. — The French breeder 
and author, Cornevin, practiced in-breeding with swine, 
cattle and sheep for considerable periods without injury. 
He in-bred Jersey cattle for seven years, Hollander cattle 
for twelve years, and Merino sheep eleven years without 
observing any evidences of degeneracy. His experi- 

1 Cornevin, "Traite de Zootechnie Generale " (1891). 



230 THE BREEDING OF ANIMALS 

ments with swine were unfavorable to the practice of 
in-breeding. According to Cornevin, among pigeons it 
is the rule for brother and sister to mate. The same 
is also generally true of ducks, geese, guinea fowls 
and swans. After eleven years of in-breeding pigeons 
and geese, he was unable to observe any changes in 
color, weight or fecundity which could be ascribed to 
in-breeding. 

Georg Wilsdorf,^ the German authority, has found 
by investigation that most pure breeds have resulted 
from in-breeding. He says, " In our studies of the his- 
tory of various breeds, we next made the astonishing 
discovery that the best living individuals belonged to 
families which, when their pedigrees were traced, were 
found all to come from a single family — often from a 
single individual. By way of illustration I might cite 
the Hanoverian halfbloods, which we know particularly 
through the studies of de Chapeaurouge and Grabensee 
to have come almost altogether from three stallions, of 
which Norfolk has hitherto had the greatest influence on 
the breed — an influence that is increasing all the time. 
Researches into the swine breeding of the Visselhovede 
district, and into that of Hildesheim in Bavaria, have 
shown that in each case a single boar was the ancestor 
of various valuable families, to-day widely scattered. 
And Hoesch of Neukirchen has found that his valuable 
strain of swine is principally due to the blood of a single 
early boar Richard." 

" The modern science of breeding, however, stands 
firm in its belief that for the production of definite types 
for special purposes in-breeding is the quickest and most 
certain method of procedure, and all great breeders who 

1 Journal of Heredity, March, 1915, pp. 110-111. 



IN-BREEDING 231 

work toward any particular goal depend largely on in- 
breeding, knowingly or unknowingly." ^ 

215. Weismann's and Von Guaita's experiments. — 
Weismann ^ in-bred mice for twenty-nine generations. As 
shown in the following table, there was a constant and 
fairly uniform decrease in fertility from the first to the 
last generation : 

1 to 10 generations ; 1345 young ; 219 litters ; avg. per litter 

6.1 

11 to 20 generations; 252 young; 62 litters; avg. per litter 

5.6 

21 to 29 generations ; 124 young ; 29 litters ; avg. per litter 

4.2 

The average number of young to a litter decreased from 
6.1 in the first ten generations to 4.2 in the last ten genera- 
tions. Whether this decrease is due directly to the specific 
action of in-breeding on the quality of fertility, or whether 
it simply represents an intensification of an innate tend- 
ency to low fertility which existed in this particular strain, 
it is not possible to determine. Von Guaita, working 
with the same strain of mice and beginning with the 
last generation (29th) bred by Weismann, obtained the 
following results : 

1st and 2d generations, avg. per litter, 3.5 
3d and 4th generations, avg. per litter, 3.6 
5th and 6th generations, avg. per litter, 2.9 

There is here a clear loss of fertility from an average 
of 6.1 to a litter to 2.9 to a litter in 35 generations, trace- 
able to in-breeding. 

1 Georg Wilsdorf, "Tierzuehtung," 1912. 

2 "Berichte der Naturforschenden Gesellschaft zu Freiburg," 
1900. 

See Morgan, "Experimental Zoology," p. 188. 



232 THE BREEDING OF ANIMALS 

216. Researches of Ritzema Bos. — An interesting 
experiment with in-breeding white rats for thirty genera- 
tions is reported by Ritzema Bos.^ Beginning with an 
albino female mated with a wild rat, the first mating re- 
sulted in twelve offspring. Seven of this litter were 
bred to a white male but unrelated. The resulting off- 
spring were closely in-bred for six years. The matings 
were brothers to sisters and parents to offspring. The 
average size of the litters for twenty generations and 
covering a period of four years remained practically 
constant. The last ten generations born during the 
last two years of the experiment showed a decided decrease 
in the fertility of the matings. The average size of 
litters by years is shown in the table. 

Decreased Fertility Due to In-breeding. (Bos) 



1887 


1888 


1889 


1890 


1891 


1892 


7i 


71 


'712 

7t7 


6fi 


4tV 


3i 



Not only the average size of the litters decreased in 
thirty generations from 7J to 3j, but the number of mat- 
ings which were sterile increased greatly from the first 
to the last generations, as shown in the following table : 

Matings Which Proved Sterile. (Bos) 



1887 


1888 


1889 


1890 


1891 


1892 





2.63 


5.55 


17.39 


50 


41.18 



There is evidence also in this experiment that the 
constitutional vigor of the offspring of parents which 
were the result of long-continued in-breeding was materi- 
ally injured. The time of the appearance of weakness 

1 Ritzema Bos, "Biol. Centralb.," XIV, 1894. See alsoMor- 
gan, "Experimental Zoology," p. 188. 



IN-BREEDING 233 

in the offspring was coextensive with the decHne in 
fertihty. 

The comparative mortaHty of the young increased 
rapidly, as shown in the following table : 

Increased Rate of Mortality Due to In-breeding. (Bos) 



1887 


1888 


1889 


1890 


1891 


1892 


Per cent 


Per cent 


Per cent 


Per cent 


Per cent 


Per cent 


3.9 


4.4 


5.0 


36.7 


36.4 


45.5 



The bad effects from in-breeding were more noticeable 
when brother and sister were mated than when parents 
were mated with offspring. Of the matings between 
parent and offspring 21.4 per cent were sterile, while 
those between brother and sister were 36 per cent infertile. 
A tendency to decrease in size is indicated by the record 
of weights of different generations. Full-grown male 
rats of the first generation weighed 300 grams each. In 
the tenth generation the weight had decreased to 275 
grams and at the end of six years the weight of rats had 
declined to 240 grams. 

217. The Wistar Institute experiments. — Extensive 
in-breeding experiments by Helen Dean King ^ at the 
Wistar Institute, Philadelphia, with white rats seem to 
have resulted in disproving the theory that in-breeding 
is always and necessarily followed by evil results. In 
this investigation white rats have been as closely in-bred 
as possible for twenty-two generations. More than 
10,000 in-bred rats have been observed during a period 
of seven years. The original stock was two pairs of 
albino rats. Each pair was used as the foundation for a 
series of in-breeding experiments. In each generation 

1 Journal of Heredity, vol. 7 (1916), p. 70. 



234 THE BREEDING OF ANIMALS 

the best rats from the standpoint of size, vigor, fecundity 
and general quaHty were carefully selected. 

The actual results of this investigation after twenty- 
two generations of in-breeding are that the male in-bred 
rats are about fifteen per cent heavier and the female 
in-bred rats about three per cent heavier than stock rats. 
The size of litters among the stock rats has been seven, 
while among the in-bred rats the litters have increased 
and now average seven and four-tenths each. The thrift 
and vigor of in-bred rats in these experiments was appar- 
ently not injured by in-breeding. " The results so far 
obtained with these rats," says Dr. King, " indicate 
that close in-breeding does not necessarily lead to a loss 
of size or of constitutional vigor or of fertility, if the 
animals so mated come from sound stock in the beginning 
and sufficient care is taken to breed only from the best 
individuals." 

218. In-breeding Berkshires by Mr. Gentry. — The 
remarkable success which may follow the practice of 
in-breeding when intelligently conducted by a skillful 
breeder is shown in the experience of N. H. Gentry of 
Sedalia, Missouri. Probably no American breeder has 
been so successful in developing all those desirable qualities 
in Berkshire swine which give this breed its great economic 
value. At the Chicago World's Fair in 1893 Gentry's 
Berkshires won twenty-three of the twenty-eight first 
prizes offered, and many of the other winners were de- 
scended from stock bred by him. At the St. Louis World's 
Fair in 1903, all the Berkshires which came within the 
five cash prizes offered, with three exceptions, were de- 
scended from animals bred by Gentry. The entire 
Gentry herd was strongly in-bred, carrying a very high 
proportion of the blood of Longfellow. Describing his 



IN-BREEDING 235 

breeding practice, Gentry says:^ *'It has long been con- 
ceded that Longfellow 16,835 was the greatest boar known 
to the breed, in this country at least. He was out of an 
imported sow and one of the best I ever saw. His sire, 
Charmar's Duke 13,360, I bred, and he was a great one, 
too. He was sired by an imported boar and was out of 
an imported sow, and this sow and the dam of Longfellow 
were got by the same boar. After the death of Charmar's 
Duke 13,360, which happened when he was only a two- 
year-old, I kept his best son, Longfellow, and after I^ong- 
fellow's death his best sons, and after their death, their 
best sons. Thus Longfellow, Longfellow's sons, and now 
his grandsons, have followed each other in use on my herd. 
One of the largest and best boars I have ever produced, 
one which I showed at the World's Fair at Chicago in 
1893, weighing at 13 months and 6 days of age, 660 pounds, 
with as much action, strength, vigor and masculine 
development as any boar I ever saw, was produced by a 
son of Longfellow out of a daughter of Longfellow sired 
by the sire of Longfellow. Thus the three top successive 
sires in his pedigree were the sire of Longfellow, Longfellow 
and a son of Longfellow. I could name many good ones 
bred as closely and, in fact, almost every animal in my 
herd has been produced by as close in-breeding on both 
sides." (See Plate XV.) 

" I have practiced in-breeding more from necessity 
than from any other reason. I believe I have not used a 
boar other than my own breeding for twenty years." 

After a lifetime's experience with in-breeding the 
conclusions of Gentry are significant : " If it is true that 
in-breeding intensifies weakness of constitution, lack of 
vigor, or too great fineness of bone, as we all believe, is 

1 Gentry, Amer. Breeders' Assoc, vol. I, 1905, pp. 170-171. 



236 THE BREEDING OF ANIMALS 

it not as reasonable and as certain that you can intensify 
strength of constitution, heavy bone, or vigor, if you have 
those traits well developed in the blood of the animals 
you are in-breeding ? I think I have continued to improve 
my herd, being now able to produce a larger percentage 
of really superior animals than at any time in the past ..." 

Another noted breeder of Berkshires who attributes 
the high quality of his animals to the practice of in-breed- 
ing is A. J. Lovejoy of Illinois. He is quoted in Daven- 
port's " Principles of Breeding " as follows : 

^ " We are believers in quite close, even in-breeding. 
We find the greatest show animals are closely in-bred. 
Sires to half-sisters is the most common form of close 
breeding, though cousins, nephews, and nieces, and even 
brothers and sisters are bred together with great success. 
It of course requires good judgment in mating animals 
that are particularly strong in individual merit. Should 
each have a bad defect in any way, we should expect 
that to be more manifest in the offspring than in the par- 
ents, and likewise the good points would be better; so 
if one mates equally good specimens the produce will be 
an improvement. There is no sire of any breed so pre- 
potent as an in-bred sire. When we get to the point 
where we feel the need of outside blood we mate an im- 
ported sow with our best boar, and from this litter we 
select a boar to use on the get of his own sire from other 
sows in the herd ; that is, we breed this boar on his own 
half-sisters." 

219. In-breeding com. — Many of the principles which 
are now universally accepted as guides to practice in 
animal-breeding were first discovered by plant-breeders. 
The mendelian principle is a good example of this fact. 

1 Davenport, "Principles of Breeding," p. 625. 



IN-BREEDING 237 

While the fundamental principles governing the trans- 
mission of characters are the same in plants and animals, 
the practical applications are sometimes widely different. 
Wholesale advice based wholly upon plant investigations, 
therefore, and intended to guide the practical breeder 
of animals is not always justified for obvious reasons. 
The experiments conducted for the purpose of testing 
the effects of in-breeding on Indian corn {Zea Mays) have 
been extensive. In every case, so far as the author has 
been able to determine, in-breeding corn has resulted in 
decreased yields if long continued. Hayes ^ and East 
found that " the first generation of in-breeding has the 
greatest detrimental effect." The injury from in-breed- 
ing is not continuous, but results in separating the pure 
lines in a variety. When once a pure line is produced 
by in-breeding, further in-breeding apparently does not 
reduce the yield. Shamel ^ found that four generations 
of self-fertilization of corn so weakened the strain that 
the seed failed to germinate. Darwin, experimenting 
with morning glories (Ipomsea) for a period of ten years, 
found that the strain which was screened so that insects 
could not bring about cross-fertilization lost in vigor 
as compared with a similar strain which had beeen left 
in the open and cross-fertilized through the agency of 
insects. 

Wheat is a self-fertilizing plant. Unnumbered genera- 
tions of in-breeding seem not to have decreased its vigor 
or lowered its fertility. Castle in-bred brother and sister 
of Drosophila (pomace fly) for 59 generations. No loss 
of fertility or vigor was observed. 

1 Hayes and East, Bui. 168, Connecticut Agricultural Experi- 
ment Station, p. 11. 

2 Shamel, U. S. Dept. of Agr., Year Book, 1905, p. 388. 



238 THE BREEDING OF ANIMALS 

Among the domestic animals it is quite probable that 
the effects of in-breeding on different species will differ 
materially. 

220. How long is it safe to continue in-breeding. — 
If we limit the application of the term in-breeding to mat- 
ings between parent and offspring or between brother 
and sister, then we cannot escape the conclusion that 
long-continued in-breeding results in decreasing fertility, 
and probably also weakens the constitution and decreases 
the size of the offspring. ^ " Continued in-breeding," 
says Kraemer, '' always must result in weakened con- 
stitution through its own influence." But such results 
follow long-continued in-breeding. What are the limits 
of safety? How long may the domestic animals be 
closely in-bred without injury? An answer to these 
questions is only possible when all the conditions are 
known, including a knowledge of the inherited tendencies 
of the in-bred animals. But it seems entirely safe to 
conclude from the evidence available that the almost 
universal prejudice against the practice of in-breeding 
is in a large degree unwarranted. Such a prejudice 
has undoubtedly limited the usefulness of many valuable 
breeding animals and has caused real economic loss to 
many breeders. 

221. Selection important. — The practice of in-breed- 
ing will never be successful in the absence of rigorous 
selection. As the undesirable qualities are transmitted 
with the same intensity as the good, constant vigilance 
is required to guard against bringing forward latent char- 
acters which are less desirable. Particularly animals 

^ Kraemer, "Mitteilung der Deutsches Landwirtschafts 
Gesellschaft," September, 1913. See also Journal of Heredity, 
1914, p. 226. 



IN-BREEDING 239 

which are undersize, weak in constitution, or that show a 
tendency to low fertihty should not be in-bred. It is 
not always possible to detect the presence of these tend- 
encies in a single generation, hence a knowledge of family 
history and pedigree is important. Given an animal 
of unusual merit with strong constitution, good size and 
strongly fertile, the breeder runs little risk in practicing 
in-breeding for a limited time. 

222. The truth about in-breeding. — In the midst of 
such diversity of opinion as exists concerning the results 
and value of in-breeding, the practical breeder may well 
be puzzled. Sweeping generalizations either for or against 
the practice are apparently unwise at this time. An 
unreasoning prejudice against the practice will result in 
withholding from breeders a valuable method of breed- 
ing which has been in many cases the chief reliance of 
the world's greatest improvers of the domestic animals. 
On the other hand, a blind following of those enthusiasts 
who have claimed for in-breeding some mysterious power 
in the improvement of animal character will certainly 
lead to disaster. 

The practice of in-breeding has been compared to a 
powerful medicine which in the hands of a skillful physi- 
cian may decide the issues of life, but in the hands of the 
novice becomes a dangerous and often fatal instrument. 
In-breeding may be practiced successfully, but only by 
those who are familiar with the biological principles 
involved, and who are familiar with the results which 
sometimes follow the mating of nearly related animals and, 
what is quite as important, who know the ancestral his- 
tory of their breeding stock. 

Whether we accept the view that evil is an incidental 
result due to the intensification of undesirable qualities 



240 THE BREEDING OF ANIMALS 

already existing in the germ-plasm of the parent stock, or 
whether we hold that certain definite evils are a necessary 
result of mating animals of near kin, we must admit that 
in-breeding has often been practiced with great success 
and no appreciable injury. It is, therefore, clearly appar- 
ent that there are conditions which are neither unusual 
nor extremely rare under which in-breeding can be prac- 
ticed with the assurance of success. 

223. Fixing characters by in-breeding. — In-breeding 
has been a powerful means of fixing and perpetuating 
valuable characteristics in the domestic animals. It is 
still a valuable method to be employed for the same pur- 
pose. But in-breeding is only a means to an end and not 
the end. In-breeding possesses no magic or occult power 
which will be exerted for the improvement of animals. 
While it works powerfully in fixing the good qualities, 
it is no less potent in firmly establishing undesirable 
qualities which may be present in the parent stock. And 
in this fact lies the chief danger from in-breeding. In 
fixing the good characters, we may unconsciously 
strengthen the powers of transmission in the direction 
of bad qualities. The most skillful breeders are less 
likely to err in the direction of perpetuating tendencies 
to evil, and history gives ample confirmation of the cer- 
tain good which does follow in-breeding when practiced 
with intelligence by skillful and experienced breeders 
and accompanied by rigorous selection. 

It has often happened in the experience of breeders that 
a sudden mutation has appeared in a single animal. This 
mutation may represent a high degree of improvement in a 
certain character or characters which the breeder has 
long sought to develop in his breeding stock. This 
variation appears in one animal only. It is highly 



IN-BREEDING 241 

desirable not only to perpetuate this improved character 
but to breed animals that have this quality in as pure 
and dominant a state as in the original animal. This 
can be accomplished by in-breeding. No other method 
is available which will so quickly and certainly result in 
producing offspring of similar or identical blood lines. 
The history of animal-breeding is rich in instances of 
great animals, famous for their individual excellence 
but more famous because they have left a heritage 
of potent '' blood " which has established a new and 
better strain or even a new breed. We need only 
recall the names of Favourite, the Shorthorn bull, Justin 
Morgan, the founder of the Morgan breed, Hambletonian 
10, the forerunner of the American trotting horse, and 
scores of individuals of lesser note belonging to practically 
every modern breed. In many of the instances to which 
reference is here made, the great individuals would never 
have become famous if breeders had not recognized their 
peculiar excellences and have insured the perpetuation 
of their valuable characters by in-breeding. 

224. In-breeding and prepotency. — The prepotency 
of animals is increased by in-breeding. There is unanimity 
among investigators and practical breeders on this point. 
By continuous in-breeding we may " breed out " less 
desirable qualities, that is, in the light of mendelism the 
characters in the germ-plasm tend to become homozygous. 
In-bred animals are " pure-bred " animals not only in the 
parlance of the breeder but also from the standpoint of 
genetics. Mating animals of diverse characters tends 
to destroy prepotency. Mixing the blood of animals of 
widely differing characteristics results in making the 
constituent characters of the germ-plasm heterozygous. 
The cross-bred animal is never prepotent. 

R 



242 THE BREEDING OF ANIMALS 

225. Results of in-breeding vary with different species. 

— The varying opinions regarding the benefits or injuries 
from in-breeding may in part be accounted for from the 
fact that investigators have based their conclusions upon 
data gathered from researches on widely differing species 
of animals and plants. The effects of in-breeding are quite 
different in different species or families. Among plants, 
nature seems to have designed some species especially to 
insure cross-fertilization and to guard against self-fertili- 
zation, while other species are self-fertilizing. Indian 
corn (Zea Mays) is a good example of the former class 
of plants. The results of continuous in-breeding on the 
maize plant are markedly injurious. Shull found that 
continual self-fertilization in Indian corn resulted in a 
loss of vigor. There are other plants like wheat that are 
self -fertilizing, and it is difficult to see how in-breeding 
can be injurious in such species. 



CHAPTER XII 
CROSS-BREEDING 

The term crossing or cross-breeding, like the term 
in -breeding, is not capable at this time of exact definition. 
In general we may define cross-breeding as the mating of 
individuals which are not related. The literature of the 
subject indicates that this term has been loosely applied. 
Some indeed have used the term to designate the mating 
of individuals belonging to different families within the 
same breed. As a rule, cross-breeding means the mating 
of individuals belonging to different breeds, as a cross 
between the Shorthorn and Hereford ; or the union of 
animals belonging to different species, as a cross between 
the stallion and the jennet. Cross-breeding has been 
strongly recommended by some breeders as a valuable 
method of improving the domestic animals. 

226. Permanent and temporary results of cross-breed- 
ing. — In recommending cross-breeding, the advocates of 
this practice have not always been careful clearly to 
differentiate between the permanent and lasting results 
of cross-breeding and the more immediate and tem- 
porary advantages. The effect of cross-breeding upon 
the purity of the heritable characters of the breed as 
represented by the germinal elements in the germ-plasm 
is one thing, while the more or less temporary effect on the 
body-cells may be quite another thing. The purpose of 
the breeder of pure-bred registered animals is to establish 

243 



244 THE BREEDING OF ANIMALS 

a race of animals that will breed true. It matters not how 
many good qualities the individual breeding animal may 
possess ; if he cannot transmit these good qualities to 
his offspring, he is not a desirable animal for breeding 
purposes. He may be valuable for commercial purposes. 
Such an animal might be a fast horse, a prize-winning 
beef animal, or a great producing cow, but lacking the 
ability to transmit these qualities this animal would not 
be a desirable or valuable individual in a breeding herd. 
It may be quite possible, therefore, for a method of breed- 
ing to have a distinct economic value for the production 
of commercial animals and at the same time be a very 
bad method for the breeder of improved live-stock whose 
purpose is to produce animals for breeding purposes and 
not for slaughter or work. What effect does cross-breed- 
ing have on the breeding powers of the domestic animals ? 
What value, if any, has cross-breeding in the production 
of animals for commercial purposes and which are not 
intended to be used for breeding ? The breeder's interest 
in cross-breeding will naturally center about the relations 
of this practice to heredity. 

227. Advantages from cross-breeding. — Breeders of 
the domestic animals have frequently practiced cross- 
breeding in the belief that certain very definite and specific 
benefits followed such practice. In attempting to analyze 
the reasons for practicing cross-breeding, it is apparent 
that this has been generally followed for one or more of 
the following reasons, — to increase fertility, to restore 
weakened constitution, to increase the size or for improve- 
ment. 

228. Grading. — The practice of grading, by which 
is meant the improvement of native or unimproved ani- 
mals by mating with pure-bred or registered animals, 



CROSS-BREEDING 245 

should not be confused with cross-breeding. Cross- 
breeding is the union of two or more distinct races or 
breeds, while grading is an attempt gradually to develop 
a type by continually breeding to pure-bred sires. 

Grading is one of the most successful and certain 
methods of improvement. There are many examples 
of successful grading among the breeders of domestic ani- 
mals. Manifestly the more inferior the foundation mother 
stock, the greater will be the improvement when mated to 
a pure-bred registered sire. A few generations will often 
suffice to produce " high-grade " cattle, horses, sheep or 
swine that will possess most of the valuable qualities 
which have commercial value. For commercial or eco- 
nomic purposes, the high-grade beef animal may be as 
valuable as the pure-bred. A high-grade dairy cow will 
often produce as much milk and butter as the registered 
cow. For breeding purposes, the pure-bred registered 
animal is far superior. The grade does not transmit its 
qualities with certainty. One object of pure breeding 
is to develop the quality of prepotency, and this is accom- 
plished by long years of most careful selection and mat- 
ing. The grade animal cannot possibly possess the 
quality of prepotency to the same extent as the pure- 
bred form, hence it follows that even if the grade does 
exhibit a high degree of individual merit, this is no evi- 
dence of ability to transmit the same qualities to the 
offspring. A high degree of individual excellence in a 
pure-bred registered animal is more certain to be trans- 
mitted, and for this reason the registered animal of high 
merit is often held by the experienced breeder at values 
which seem beyond any real economic basis. 

229. Cross-breeding to increase fertility. — Some ani- 
mals are infertile when bred to other individuals of their 



246 THE BREEDING OF ANIMALS 

own breed. This is particularly the case if the two ani- 
mals mated are the result of long-continued in-breeding 
and are themselves also near of kin. 

In the instance of in-breeding pigs by J. Wright already 
cited, the seventh generation resulting from close in- 
t)reeding consisted of one sow. This sow was infertile 
when bred to her sire, but bred readily with an unrelated 
boar. Darwin cites numerous instances of increased 
fertility due to crossing. Mr. Eyton,^ a breeder of Grey 
Dorkings, found it necessary to increase the prolificacy 
and increase the size of his in-bred stock by cross- 
ing. Bates,^ the great breeder of Shorthorn cattle, bred 
closely in-and-in for thirteen years, but then found 
it necessary to " infuse fresh blood, not to improve 
the form of the animals but on account of lessened 
fecundity." 

Bloodhounds ^ closely in-bred lost their fertility, which 
was restored by a single cross. 

Many plants are infertile unless cross-fertilized with 
the pollen of another variety. 

230. Cross-breeding to increase size and restore 
constitution. — The tendency of in-breeding to decrease 
the size is promptly corrected by cross-breeding. " The 
good effects of a cross are at once shown by the greater 
size of the offspring." 

It is the common experience of breeders that highly 
improved strains of cattle, hogs or sheep sometimes show 
a refinement or delicacy of constitution which in a measure 
interferes with the economic value. In such cases a sud- 
den out-cross to another equally valuable strain may 

^ Darwin, "Animals and Plants under Domestication," vol. 
II, p. 105. 
2 Ibid. 
' Loc. cit. 





^>. 



y >. 









CROSS-BREEDING 247 

quickly correct any tendency to inferior size or weakened 
constitution. Not only are in-bred animals benefited 
in certain definite qualities by crossing, but breeds and 
families which have not suffered in any way from in-breed- 
ing are sometimes improved in size, vigor and fertility 
by crossing. 

231. Crossing and heredity. — As in-breeding tends 
to simplify the germ-plasm and strengthen the powers of 
transmission, so cross-breeding tends to weaken the 
prepotency and complicate the elemental constitution 
of the hereditary substance. Crossing has a tendency 
to break up established characters. It destroys com- 
binations of characters which have long existed in the 
strain and which under systems of pure breeding have 
behaved in a manner like unit characters in trans- 
mission. The result of crossing pure-bred animals is 
often to destroy the results of generations of careful 
breeding and selection. 

232. First cross an improvement. — The cross-bred 
offspring of pure-bred parents often show an improvement 
over either of the parents. This superiority may be 
exhibited not alone in increased fertility and more vigorous 
constitution, but also in the very qualities which char- 
acterize the parents. A cross between animals belong- 
ing to distinct breeds may be a better beef animal than 
either parent. The Scotch farmer breeds the Aberdeen 
Angus cow to a white Shorthorn bull. The offspring is 
the well known " blue gray " which is highly prized by 
the feeder and in the fat cattle market commands a 
premium over the pure-bred animals of either breed. 
The fat cattle exhibitions of the world have not infre- 
quently given the highest prizes of the show to cross- 
bred animals. (See Plate XVI.) 



248 THE BREEDING OF ANIMALS 

But when it is attempted to perpetuate the superior 
qualities of the cross-bred animal by breeding, disappoint/- 
ment invariably results. The second cross resulting 
from the mating of two cross-bred animals may be totally 
unlike either of the immediate parents or of the original 
pure-bred forms. Crossing, therefore, is not a method to 
be employed for rapid improvement or for fixing desir- 
able qualities. It is opposed to in-breeding which does 
increase prepotency and is the most rapid method known 
of fixing desirable characters. 

233. Cross-breeding as a cause of variation. — The 
fact that crossing disturbs the balance of characters and 
brings about recombinations in the germ-plasm gives it a 
peculiar value in causing variations to appear. The 
breeder who is working with pure-bred animals which owe 
their purity of breeding to a long period of careful selec- 
tion by skillful breeders cannot hope to cause any great 
degree of improvement. Pure-bred animals are already 
improved. About all any breeder working with pure- 
bred animals can do is to select out the highly desirable 
strains from those of lesser value already in the breed. 
But as Johanssen has shown, there are very definite limits 
beyond which the improvement of pure lines cannot go. 
Marked improvement must come through variation. 
Crossing is a common cause of variation. Variations 
which appear as the result of crossing may be desirable 
or undesirable. They may be relatively unimportant 
or they may be in the nature of a valuable mutation. 
Such valuable mutations may be perpetuated by in -breed- 
ing and a new and valuable quality sometimes secured 
in this way. This method is not practical for breeders 
of registered live-stock under present conditions, but has 
been of great service to the breeders of plants. 




Plate XVII. — Upper. — Half-blood buffalo (bison) heifer. The 
hybrids are larger than either parent. Lower. The bull on the left is 
five-eighths buffalo (bison) and three-eighths Hereford. The animal on 
the right is a three-quarter blood buffalo. These hybrids are frequently 
sterile. 



CROSS-BREEDING 249 

234. Crossing species. — Many species may be suc- 
cessfully crossed. Some of these crosses are of great 
economic value, as the cross between the mare and the jack. 
The number of successful crosses between animal species 
is not large. Such unions are difficult to make and 
generally sterile. When such crosses are possible and 
the union is fertile, the offspring is generally partially 
or wholly sterile. Some of the successful crosses which 
have been reported are the sheep and goat, horse and ass, 
horse and zebra, cattle and yak, cattle and bison, brahmin 
and domestic cow, game cock and guinea fowl, domestic 
fowl and pheasant, dog and wolf, and dog and fox. 

235. Crossing bison and cattle. — A most interesting 
experiment in cross-breeding between the bison and 
domestic cattle is reported by Mossom M. Boyd.^ The 
hybrid offspring from Hereford dams and bison sire were 
very uniform, all having white faces, were larger than 
the bison and much smoother, broader and deeper than 
the sire. Great difficulty was experienced in making 
the first cross from the excessive secretion of the amniotic 
fluid. This difficulty caused many deaths. The per- 
centage of males from the first cross was very small. 
Among forty-five hybrids, only six were males. Of these 
three died at birth, one died in less than twenty-four hours 
after birth, one proved barren, and the last male was 
killed before determining his fertility. Charles Good- 
night of Texas reports ^ that " no male calves have ever 
been born ; cows conceiving them either suffer abortion 
or die, hence only get heifer calves and only a small per 
cent of them." The hybrids produced their first calves 
at an average age of five years (Plate XVII). 

1 Boyd, Journal of Heredity, 1914, p. 189. 

2 Goodnight, Journal of Heredity, 1914, p. 199. 



250 THE BREEDING OF ANIMALS 

Three-quarter blood bisons from pure bisons, bulls and 
hybrid cows were similar in form and color to the bison ; 
one cross-bred from a half Hereford dam had a white 
face. One-quarter blood bisons from hybrid dams and 
Hereford and Aberdeen Angus bulls were uniform in 
conformation but varied in color. The three-quarter 
bloods closely resembled the bison, while the one-quarter 
bloods could not readily be distinguished from domestic 
cattle. From twenty-four hybrid cows, only three were 
regular breeders and fifteen were barren. From twelve 
one-quarter blood bison cows bred to domestic animals, 
seven were fully fertile, four were irregular breeders, and 
one was barren. One out of four of the three-quarter 
blood bison cows was barren. The term '' cattalo " 
is used by Boyd to designate the third generation. When 
both parents are of mixed blood, the cattaloes are in many 
respects superior to ordinary domestic cattle, being hardier 
and much less subject to disease. Cattaloes with a high 
percentage of bison blood are probably immune from 
Texas fever and blackleg. The cattalo grows to a greater 
weight than domestic cattle. Goodnight ^ says, " More 
of them can be grazed on a given area. They do not 
run from Heel Flies nor drift in storms. They rise on 
their fore feet instead of their hind feet. They never 
lie down with their backs down hill, so they are able to 
rise quickly and easily." 

It seems entirely probable that a new breed will be 
added to the list of domestic cattle, and if this result is 
achieved, it will be one of the very few authentic cases of 
the establishment of a new breed by crossing species. 

236. The mule hybrid. — The most widely distributed 
and most useful hybrid known is the mule, which is pro- 

^ Goodnight, Journal of Heredity, 1914, p. 199. 



CROSS-BREEDING 251 

duced by crossing the domestic mare to the jack. In 1915 
there were 4,479,000 mules in the United States. This 
was more than one-fifth of the total number of horses 
in the country at the same time. The production of 
mules has increased at a more rapid rate than horses, and 
the use of mules is becoming more extensive. The mule 
hybrid is a remarkable example of the practical advantages 
which follow a particular cross. This animal is more 
hardy and enduring than either parent. As compared 
with the horse, the mule is longer-lived, less subject to 
disease or injury, and more efficient in the use of food. 
The mule can be safely put to work at a younger age, will 
thrive on coarser feed, and seems to be much better able 
to avoid many dangers which menace the usefulness of 
the horse. The mule will perform more arduous labor 
on less food. The mule will endure the heat of southern 
latitudes more successfully than the horse and is there- 
fore a popular draft animal in the South. 

The cross between the mare and jack is readily accom- 
plished and the union is perfectly fertile. The conforma- 
tion of the mule more closely resembles that of his sire. 
The ears are long, feet long and narrow, withers sharp, 
mane and tail scanty, and the voice a bray like the jack. 
The mule is sterile. A few cases of supposed fertility of 
mare mules have been reported, but the writer has investi- 
gated several apparently reliable reports and has never 
found an authentic case of a fertile mule. Most of the 
erroneous reports of fertile mules have apparently arisen 
from the not infrequent cases of mare mules which have 
been observed suckling mule foals. The milk glands of 
mare mules have been known to function as the result 
of the stimulation afforded by a suckling foal. A case 
of a mare mule giving milk was reported to the writer 



252 THE BREEDING OF ANIMALS 

by L. O. Swarner of Boonville, Missouri, in 1913. This 
mare was six years old and at the time had been giving 
milk for five weeks. The milk glands had not been stimu- 
lated in any way, but the milk " streamed " from the 
udder. It is also of interest to know that this mare mule 
showed unmistakable evidences of what in the ordinary 
mare would be regarded as complete sexuality. She 
came in heat regularly. The mule was bred frequently 
when in season to both the stallion and jack, but failed 
to conceive. A sample of the milk was analyzed by the 
Chemical Department and found to contain 2.46 per cent 
protein, 5.8 per cent sugar, 1.45 per cent fat, and .4 per 
cent ash. (See Plate III.) 

The mare mules apparently have all the essential 
organs of reproduction and come in heat with considerable 
regularity. The horse mule also has the essential sexual 
organs well developed and his sexual instincts are so well 
developed that castration of young mules is universally 
practiced. The cause of sterility in the horse mule is not 
due to a failure to develop spermatozoa, but the sperm- 
cells are imperfect. In some cases the sperm-cells lack 
the tail or fl^gellum. 

237. The hinny hybrid. — The reciprocal cross between 
the jennet and the stallion is accomplished without 
difficulty and the union is very fertile. The hybrid from 
the cross is called a hinny. Some authorities have held 
that the hinny resembled the horse much more closely 
than the mule, but this is denied by most practical breeders. 
The hinny is not commercially important as the jennet 
is too valuable for the production of jacks to be used for 
crossing. The hinny is sterile. (See Plate XVIII, upper.) 

238. Crossing the horse and the zebra. — The horse 
and zebra have been successfully crossed by Ewart of 





Plate XVIII. — Upper. A five-year-old hinny. Dam a jennet, 
sire a Percheron stallion. Lower. Sheep-goat hybrid. 



CROSS-BREEDING 253 

Edinburgh, Scotland, the United States Department of 
Agricuhure and many others. The zebra-horse hybrid 
is easily domesticated and can be successfully broken 
to harness. The first cross is not so easily made as that 
between the jack and the mare but is not impossible or 
extremely difficult. The zebra possesses a much smoother, 
finer and more horse-like form than the ass, and the 
zebra hybrid therefore is possessed of more quality and 
" finish " than the mule. This hybrid should prove 
valuable, particularly in those regions where the " tsetse " 
fly is fatal to horses but not to zebras and probably not 
to the zebra hybrids. 

239. Crossing cattle and. zebu. — Many crosses have 
been made between the zebu and European cattle and 
between the zebu and the cattle of Tunisia. The first 
cross in practically all of the experiments seems to have 
been successful. 

The cross-bred zebu is resistant to Texas fever and 
anthrax and is not seriously inconvenienced by foot and 
mouth disease.^ In Brazil ^ the zebu cross is popular. 
It is claimed that the cross-bred zebu is more prolific and 
that these animals herd together better than the ordinary 
domestic cattle. The zebu hybrids are less tractable 
and docile than domestic cattle, but are very active and 
enduring draft animals. « 

Because of the disease-resisting qualities of the zebu, 
its prolificacy, adaptability to hot climates and general 
hardiness, Nabours ^ is of the opinion that this type of 
cattle may yet become an important breed in the United 
States. 

1 Roederer, Journal of Heredity, 1915, p. 201. 

2 Hunnicutt, Journal of Heredity, 1915, p. 195. 

* Nabours, American Breeder's Magazine, 1913, p. 38. 



254 THE BREEDING OF ANIMALS 

240. Sheep-goat hybrid. — The cross between the 
sheep and goat has been successful in a number of in- 
stances. Spillman reports such a hybrid belonging to E. 
Armand of Monett, Missouri. (See Plate XVIII, lower.) 

The covering of the body of this hybrid was generally 
goat hair, but the back was covered with '' shaggy wool." 
" This hybrid is a female and appears to be infertile, but 
not absolutely so, for it has once produced a half-grown 
foetus." 1 

1 Spillman, Journal of Heredity, 1913, p. 69. 



CHAPTER XIII 

DEVELOPMENT 

The qualities which an animal possesses are due in 
the first place to inheritance and in the second place to 
the manner in which the inherited qualities have been 
developed. An animal cannot develop beyond the capaci- 
ties which have come to it through the germ-plasm. It 
is also true that the capacities which are inherited cannot 
benefit the individual unless they are developed through 
a favorable environment. It is seldom that an animal 
realizes fully the possibilities for development which are 
inherent in the germ-plasm. The carefully bred beef 
animal inheriting those valuable qualities of early ma- 
turity, broad, deep and rounded form, rugged constitution 
and quiet temperament, with a distinct tendency to lay 
on fat when food is abundant, may completely fail to 
exhibit these inborn characters and actually display the 
form and characteristics of the unimproved animal if it 
has been surrounded by conditions which are unfavor- 
able for the development of these special qualities. The 
highly improved dairy cow with the inherited capacity 
to produce enormous quantities of milk and butter may 
never rise above mediocrity if she is not supplied with 
food and her milking functions intelligently developed. 
In the selection of animals for improvement, the skillful 
breeder can never know what results he has achieved 
until the products of his skill have been fully developed. 

255 



256 THE BREEDING OF ANIMALS 

It is not too much to say that no man can be a successful 
breeder who is not also skillful in developing his animals. 
Thus, in practice, development becomes supremely im- 
portant and throughout the history of animal-breeding 
has been only second in importance to heredity itself. 
A satisfactory treatment of development in all its phases 
as related to animal husbandry would require a volume, 
and as the chief purpose of this work is to consider how 
the inherited capacities of animals finally appear as definite 
characters in the germ-plasm, only a limited reference 
can be made to developmental phases of chief importance 
to the animal-breeder. 

241. Growth. — From the fertilization of the egg until 
the full development of the mature individual, the animal 
increases in volume and changes in form. This increase 
and change of form is called growth. The final size of 
an animal is determined by the rate of growth and the 
length of the growth period. The guinea pig and rabbit 
come to full maturity at about the same age, but the rabbit 
is larger because its rate of growth is more rapid. The 
rate of growth in the rabbit and man is about equal, 
but man is much larger at maturity because the period 
of growth is much longer.^ 

242. The growth impulse. — The young of any species 
tend to develop and grow in accordance with the normal 
habit of the species. This applies in a special sense to 
the skeletal system. Even in the absence of a sufficient 
supply of feed and other favorable conditions, the young 
animal displays a remarkable physiological impulse to 
continue to increase in the skeletal parts. ^ Animals fed 

1 Morgan, "Experimental Zoology," p. 245. 

2 Waters, "Capacity of Animals to Grow under Adverse 
Conditions." 



DEVELOPMENT 257 

on a limited ration will continue to increase in height, 
length of body, and other parts of the skeleton, at the 
same time becoming thinner and thinner in flesh. Even 
during starvation the same tendency is apparent. This 
fact has been noted by H. Aron,^ who found that while 
fasting, the skeleton grows at the expense of the other 
body tissues. 

243. Factors influencing growth. — The chief factors 
influencing growth in the domestic animals are food, 
heat, light, age, gestation and lactation. The chief 
condition influencing growth in normal animals is the 
food supply. 

244. Growth and food supply. — While it is true that 
the animal may for a limited time add to its tissues when 
food is insufficient in either quantity or quality, it is 
also tru^ that a long-continued deficiency in the food 
supply of young growing animals will invariably check 
their growth. The check to growth in such cases may 
be only temporary, or it may result in permanently decreas- 
ing the normal size of the mature animal. (See Plates XIX 
and XX.) 

245. Capacity to grow. — The young animal that is 
stunted as a result of insufficient food does not lose the 
capacity to grow. The organism seems to be able to 
continue to function and maintain a certain equilibrium. 
If later a greater abundance of food is supplied, the rate 
of growth may be reestablished. If after a period of 
partial starvation the food supply is abundant, the rate 
of growth may for a time be even more rapid than before. 
That the capacity of an animal to grow is not destroyed 
by stunting is shown by the results of an investigation 
at the Missouri Experiment Station by Waters and 

1 H. Aron, Exp. Sta. Record, vol. 24, p. 765. 

s 



258 THE BREEDING OF ANIMALS 

P. F. Trowbridge.^ These investigators fed a beef steer 
from the age of three months to thirty-eight months old. 
From three to twelve months of age the animal was fed 
on a maintenance ration (Plate XXI). An attempt was 
made to feed the young calf in such a way that it would 
neither gain nor lose in live weight. At the beginning of 
the period (three months old) (Plate XXI, upper left) 
the animal weighed 175 pounds; at twelve months 
(Plate XXI, upper right) the animal weighed 212 pounds. 
Another animal similar in every way at the beginning 
was fed a full ration of nutritious feed. The latter 
animal increased in weight from 200 pounds at four 
months (see Plate IX) to 875 pounds at 336 days of 
age (Plate VIII, upper). The animal fed on a sparse 
ration continued to increase in height, length of body, 
size of bone, and other skeletal measurements but lost 
constantly in fat and gradually became leaner and thinner. 
At the end of the twelve months the steer was much 
emaciated and showed symptoms of starvation. From 
the standpoint of the practical feeder, the animal was. 
clearly stunted in its growth, and in the opinion of many 
breeders he had lost very greatly in his capacity to gain 
in live weight and to do so on what would be regarded as 
a normal amount of food. In other words, his economic 
value for the production of beef was very greatly dimin- 
ished. After twelve months the animal was given a 
gradually increasing amount of nutritious food until 
he was consuming a normal ration. The animal rapidly 
improved in condition and at twenty-four months (Plate 
XXII) had reached a total weight of 1055 pounds, a total 
gain of 842 pounds in twelve months. This gain was not 
expensive in that a large amount of feed was required to 

1 Missouri Experiment Station, unpublished data. 






Plate XXI. — Starvation does not destroy capacity to grow. Upper 
left. Steer 529 weighing 175 pounds at age 96 days. Ration greatly 
restricted until age 365 days. Upper right. Steer 529 weighing only 
200 pounds at age 310 days. Resulting from feeding greatly restricted 
ration. Lower. Same animal at age 38 months and weighing 1487 
pounds. 




a >.^ 

fed -t^ s 



c3 



I— I t3 

o3 c3 ^M 

^ M 

►J ^ g bc 



DEVELOPMENT 259 

produce a pound of gain, but on the other hand the gain in 
live weight was accompHshed by feeding only five and six 
one-hundredths pounds of grain and two and four-tenths 
pounds of hay for each pound of gain. The steer that 
had been fed generously for the first twelve months of 
its life gained only 500 pounds during the period in 
which the stunted one had gained 842 pounds. In the 
production of the 500 pounds the full-fed steer had con- 
sumed nine and eight-tenths pounds of grain and four 
and two-tenths pounds of hay for each pound of gain in 
live weight. Over forty per cent less feed was required by 
the stunted animal for each pound of increase in live 
weight. Not only did the stunted animal not lose 
its capacity to grow, but in certain respects its growth 
processes were accelerated during the period covered 
by this experiment as a result of its difficult struggle 
for existence during the first twelve months of its 
life. 

246. Growth and the cell. — Increase in the size of 
animals which follows growth is due to a multiplication 
of cells and not to an increase in their size. The size 
of cells varies between rather narrow limits. The larger 
size of some animals is not due to larger cells in their 
organization but to a larger number of cells. It is also 
true that the cells in any individual animal vary but 
little in size. The increase in size of any part of an animal 
is due, therefore, to an increase in the number of cells 
and not to an expansion of cells already formed. It is 
true, of course, that certain minor exceptions to this rule 
are to be observed. The nerve cells vary in size with the 
size of the animal. The nerve cells of an ox are much 
larger than those of the pig. The frog has very large 
cells, while the starfish is composed of small cells. But 



260 THE BREEDING OF ANIMALS 

a large frog differs from a small frog in the number of 
cells, not in their size. Each individual animal begins its 
existence as a single cell. Through cell division the em- 
bryonic organism rapidly increases in size until maturity 
is reached. The rate of growth of the individual is most 
rapid during the very early stages in the development of the 
embryo. The rate of growth decreases gradually from this 
time until full maturity, when nominally growth ceases. 

247. When the growth impulse is strongest. — The 
growth impulse is strongest in the animal while still exist- 
ing in the uterus of the mother. After birth the growth 
continues less rapidly, but is still very rapid when compared 
with the increase in size during the later months of the 
growth period. It is for this reason that the period of 
gestation is so fundamentally important in the life of the 
animal. During this period of exceedingly rapid increase 
in size and development of the vital organs and other parts 
of the body, any abnormal condition which interferes 
with the normal requirements of the unborn animal may 
cause arrested development and result in seriously retard- 
ing the growth or permanently crippling the individual. 
It is undoubtedly true that during this period the prac- 
tical breeder may through skillful feeding and care ma- 
terially influence for good or evil the development of the 
valuable characters of the domestic animals. 

248. Development of the foetus. — The development 
of the fertilized egg through the embryonic stages of the 
life of the mammalian animal is influenced by a number 
of conditions which may have a profound influence upon 
the material well-being of the future mature animal. 
Some of these influences are as yet obscure and not well 
understood, while others are more clearly determined 
and their effects more easily recognized. 



DEVELOPMENT 261 

The development of the foetus is influenced by heredity, 
and the physiological environment of the pregnant mother. 
Among the latter are the general health or well-being 
of the mother, age, the quantity and quality of the food 
supply and mental impressions. 

249. Heredity and foetal development. — The inherited 
tendencies of an animal are exhibited from the very be- 
ginnings of its existence in the fertilized egg-cell. Its foetal 
development, therefore, must be influenced to a certain 
extent by those inherent determiners which have come to 
the fertilized egg-cell from the male parent. The size of 
the foetus at various stages of development then would be 
determined, not alone by the maternal heredity and en- 
vironment, but also by the inherited characteristics which 
have been acquired through the male. At the same time 
it is probable that the maternal environment has a much 
more important influence on the foetal development than 
its paternal hereditary tendencies. If it were otherwise, 
serious consequences might follow the mating of smaller 
females to much larger males among the domestic animals. 

Pony mares weighing 700 to 900 pounds are not infre- 
quently mated with large stallions of the draft breeds 
weighing 2000 pounds or more. Under these conditions 
the foetus is not as much larger than the normal foetus 
of the mother as might be expected from the much greater 
size of the stallion. Small burro mares weighing 400 
or 500 pounds have been artificially inseminated with 
the sperm of Percheron and other heavy draft stallions. 
The growth of the foetus in this case is undoubtedly some- 
what greater during the normal period of gestation than 
the growth of a pure burro foetus, but the increased size 
is not a mean between the normal size of a Percheron and 
a burro foetus, but is much smaller. 



262 



THE BREEDING OF ANIMALS 



Relation of Weight of Dam to Birth Weight of 

Lamb 



Weight op Dams 


Number 

OF 

Single 
Lambs 


Average 

Birth 

Weight 

OF 

Single 
Lambs 


Number 

OF Twin 

Lambs 


Average 

Birth 

Weight 

OF Twin 

Lambs 


Average 
Birth 

Weight 
OF All 
Lambs 


Below 90 lbs. . . 
90 to 100 lbs. . 
100 to 110 lbs. . 
110 to 120 lbs. . 
120 to 130 lbs. . 


8 

6 

14 

12 

13 


7.2 lbs. 
7.4 lbs. 

8.6 lbs. 

8.7 lbs. 
8.9 lbs. 


8 
20 
10 


6.4 lbs. 
7.2 lbs. 
7.6 lbs. 


7.2 lbs. 

7.4 lbs. 

7.5 lbs. 
7.9 lbs. 

8.3 lbs. 



250. Birth weight of lambs. — The author/ investi- 
gating the birth weight of lambs from grade Merino ewes 
bred successfully to Shropshire, Hampshire and Merino 
rams, found that the size of lambs at birth is primarily 
determined by the nutrition of the foetus while carried 
in the uterus of the mother. The nutrition of the foetus 
will of course be determined entirely by the physiological 
condition of the mother during gestation. This is shown 
in one test in which the birth weight of twenty-nine lambs 
sired by two heavy rams averaging 237 pounds in weight 
was 8.16 pounds. The average weight of two other 
rams of the same breeds was 142^ pounds. The two 
lighter rams sired twenty-five lambs from the same ewes, 
or ewes of the same type. The average birth weight of 
these lambs was 8.75 pounds. The weight of the sires 
in this case seemed to have little influence on the weight 
of lambs at birth. In attempting to discover the real 
factors determining the growth of the foetus as measured 
by the weight of lambs at birth, it was found that the 

IF. B. Mumford, "Some Facts Influencing the Weight of 
Lambs at Birth," Bulletin 53, Missouri Experiment Station. 



DEVELOPMENT 263 

nutritive condition and weight of the mothers had an 
important influence on the development of the foetus. 
This fact is shown in the table on page 262. 

Summarizing the results of four years' work, the author 
says/ ^' We must conclude from the exhibit here made, 
comprising the results of 61 births, that the weight of 
the mother has a direct influence upon the birth weight 
of the offspring and that in general the lambs having a 
heavier weight at birth are produced from the larger 
ewes." 

251. Effect of protein and ash in ration on fcetal 
development. — The development of the foetus may be 
materially influenced by the ration given to the mother 
during pregnancy. Evvard ^ has shown that if pregnant 
sows are fed a ration poor in protein, the pigs are smaller 
at birth. Not only were the offspring smaller at birth, 
but they were weaker and the death rate greater. The 
first investigation was made with young sows in 1910- 
1911. These were fed the rations indicated in the table 
on page 264 for a considerable period. The results are 
summarized in the table. 

^ " The basal ration was corn alone. Corn we know is 
quite deficient in protein (the zein which comprises prac- 
tically 58 per cent of said protein is peculiarly lacking in 
two quite important amino acids, namely, tryptophane 
and lysine) and calcium. It is somewhat surprising to 
know that calcium comprises practically two-thirds as 
much of the body substance as does nitrogen, the basal 
element of protein." 

" Note that the supplemented rations not only pro- 
duced larger but stronger pigs at birth. A studied survey 

^ Mumford, loc. ciL, p. 176. 

2 Evvard, Iowa Academy of Science, Report 1913, p. 326. 



264 



THE BREEDING OF ANIMALS 



of the above figures shows most clearly that even though 
the carbohydrates were limited, as in the meat meal 
lots, the increase in protein and ash was such as to mark- 
edly influence the size and strength of the new-born pigs. 
That clover and alfalfa should also have a marked effect 
is logical because these hays are leguminous in character, 
run high in protein and calcium, and also have an alkaline 
ash which is probably beneficial." 

Effect on Offspring of Feed Fed Pregnant Swine ^ 
Gilts. — Five in a Lot, 1910-1911 



Gilt Record 


Offspring Record 




a 
O 


Feed Daily 


.1 




Per cent Vigor 


















Pregnancy Ration 
OP Gilts 


> 

< 


Shelled 
Corn 
Lbs. 


Supple- 
ment 
Lbs. 


6i^ 

< 


Av. wt. 

born P 

Lbs. 


a 
B 




0) 


Q 


Corn Only . . . 


.354 


3.65 


None 


7.6 


1.74 


68 


16 


16 





Corn +Meat Meal 




















(Light) . . . 


.582 


3.21 


0.127 


7.4 


2.01 


92 


5 


3 





Corn+MeatMeal 




















(Heavy) . . 


.635 


2.75 


0.432 


8.8 


2.23 


93 


5 


2 





Corn + Clover . . 


.528 


3.67 


0.302 


6.4 


2.21 


94 





6 





Corn+Alfalfa . . 


.627 


3.74 


1.106 


7.6 


2.29 


89 


8 





3 



A similar test with older (^-earling) sows confirmed the 
conclusions from the first investigation. In the latter 
trial there was evidence that animal protein supplied in 
meat meal was more efficient than vegetable protein 
supplied in linseed oil meal. 

252. High calcium rations for pregnant swine. — The 
ordinary rations fed to farm animals in most localities 

1 Evvard, Iowa Academy of Science, Report 1913, p. 326. 



DEVELOPMENT 265 

are known to be deficient in calcium. This is particu- 
larly true when, as in the case of swine, the rations are 
chiefly composed of grain with a relatively small propor- 
tion of roughage. It is a popular notion that feeding 
pregnant farm animals a high calcium ration will cause 
the skeletal systiem of the foetus to develop even beyond 
what may be regarded as normal. As a result of this 
greater development of the skeleton, it has been alleged 
that the mother may sometimes have serious difficulty 
in expelling the foetus. Some confirmation of this belief 
is apparently found in the work of Evvard already de- 
scribed. But in this investigator's trials a ration abnor- 
mally deficient in calcium and protein is compared with 
normal rations. Adding an excess of calcium to a normal 
ration may not necessarily increase the size or change the 
composition of the foetus. In this respect we know that 
similar changes in the ration do not change the composi- 
tion of the milk. At the Wisconsin Experiment Station, ^ 
Hart, Steenbock and Fuller compared normal rations 
with a high calcium ration fed to pregnant swine. Eight 
Poland China sows were fed in lots of tw^o each. Three 
lots were fed on a high calcium ration by the addition of 
calcium carbonate, calcium phosphate (floats) and alfalfa. 
One lot was fed a normal standard ration known to be 
adequate for pregnant swine. These rations were fed 
throughout the gestation period. Although the calcium 
rations contained five times the amount of this mineral 
present in the normal ration, there was no evidence 
that the skeleton of the foetus was influenced in 
any degree. The authors in summarizing their results 

^ Hart, Steenbock and Fuller, " Calcium and Phosphorus 
Supply of Farm Feeds and their Relation to the Animal's Re- 
quirements," Wisconsin Research Bulletin No. 30. 



266 THE BREEDING OF ANIMALS 

conclude that " High calcium rations, as compared with 
low calcium rations, had no effect whatever during a 
single gestation period on the size or calcium content of 
the skeleton of the foetus. The skeleton is not increased 
in any dimension by a wide variation in the amount of 
calcium fed the mother." 

253. Size and vigor of foetus as influenced by corn and 
wheat rations. — The particular rations fed to breeding 
animals may profoundly influence the character of the 
foetus. It is not enough that the prospective mother 
should receive a ration containing the right proportions 
of protein, carbohydrate and mineral substances, but 
these minerals must be of the kind of substances which 
are known to satisfy the nutritive necessities of the ani- 
mal. A most interesting demonstration of this fact was 
made possible through the valuable work of Hart,^ McCol- 
lum, Steenbock and Humphrey at the Wisconsin Experi- 
ment Station. In May, 1907, these investigators began 
feeding four heifers a ration of corn meal, corn stover and 
gluten feed, all corn products. Another group of four 
was fed wheat meal, wheat straw and wheat gluten, nutri- 
ents derived entirely from the wheat plant. The mate- 
rials supplied in each ration were proportioned in such a 
manner as to furnish each group of animals a well- 
balanced ration in accordance with the accepted feeding 
standards. The feeding continued for two years and 
accurate records were kept of feed consumed, gains in 
live weight, and physiological condition of all animals in 
the experiment. 

1 Hart, McCoUum, Steenbock and Humphrey, "Physio- 
logical Effect on Growth and Reproduction of Rations Balanced 
from Restricted Sources," Research Bulletin No. 17, Wisconsin 
Experiment Station. 









■X- 






■■>.--s-*^-^H?ij 



.-5 - r: 



.■^. 



"/IS^'^'^* 



-A^ •-. 



--— -«„-^_ '>, , 


..,_. r -^ 


-^ T_„..^— ' 'C. ' ■ -v 




' J : '■ 


in 


^' '" ' "■"■ 


- . -*^"/ ^■* 




1 ' 


N «.^. ^^^^^m^^IRh 




r^ , ^tt 




AHflJ^^^H 




1 


« 




HH 








~ ^^^1 


P^^ 




^ ^' 


r 






r^ M 


'». '"C^^^ 


■,_>..-■ -_.',. 


:v._.:_., v.:«l 


BHfe-L-...:' 




hhh 



Plate XXIII. — Upper. A normal healthy cow in good nutritive 
condition fed exclusively on nutrients derived from Indian corn. 
Lower. This vigorous, thrifty, well-developed new-born calf from dam 
(upper) fed exclusively corn ration before and during gestation. 




Plate XXIV. — Upper. Unthrifty cow clearly in bad nutritive con- 
dition due to having been fed wheat products exclusively. Lower. Calf 
of low vitality from dam (upper) fed exclusively on wheat products, 
lived only twelve hours. 



DEVELOPMENT 267 

The rate of growth of all animals in the two groups 
was very similar, indicating little difference in the effi- 
ciency of the rations. But that there was a difference 
is indicated by the author's description : ^ " The corn-fed 
animals (Plate XXIII) looked smooth of coat, fuller through 
the barrel ; and, as expressed by experienced feeders and 
judges of domestic animals, they were in a better state of 
nutrition. On the other extreme stood the wheat-fed 
group with rough coats, gaunt and thin in appearance, 
small of girth and barrel, and to the practical eye, in rather 
a lower state of nutrition." But perhaps the most sig- 
nificant results of this experiment were the effects of these 
rations on the reproductive functions of the mothers and 
the vitality of the offspring. The gestation period in the 
corn-fed mothers was practically normal, while in every 
case the calves of the wheat-fed group were dropped 
from two to five weeks before the end of the normal 
gestation period. The calves from the corn-fed cows 
were uniformly strong and vigorous and were normal 
in every respect. The calves from the wheat-fed cows 
were all born dead or with such low vitality that they 
soon died. 

The yield of milk from the wheat-fed (Plate XXIV) 
cows was distinctly below that of the corn-fed group. In 
discussing the significant results of this investigation the 
authors say, " These results emphatically show how de- 
pressing or stimulating the influence of a ration may become, 
even when it is made up of supposedly normal feed materials 
and balanced as to ordinary chemical constituents and 
supply of energy, especially when that ration is continued 
for a long time. The evidence for the necessity of giving 
much weight to the physiological influence of the ration, 

1 Loc. cit. 



268 THE BREEDING OF ANIMALS 

apart from its digestible protein content and calorific 
value, is positive." 

254. The permanent effect of retarded growth. — Is 
the retardation of growth resulting from unfavorable 
environment a permanent condition? Is it possible per- 
manently to stunt an animal? This question is one of 
great interest to the practical breeder of live-stock and 
the live-stock farmer. The animal is often employed by 
the farmer for the purpose of disposing profitably of food 
materials which are of limited value from the standpoint 
of nutrients and digestibility, but nevertheless have a 
food value. Teachers and investigators in animal hus- 
bandry have for a long time taught that any condition 
which resulted in stunting the young animal, perma- 
nently affected the mature individual. It has also been 
claimed by some that the capacity to grow was materially 
diminished by a stunting period. 

The history of two animals which were fed at the 
Missouri Experiment Station by P. F. Trowbridge^ is of 
great interest in attempting to answer this question. One 
of these animals was given a full ration from birth and 
the other animal was given a so-called maintenance ration 
from three months of age to thirteen months. The use 
of the term maintenance ration in this connection means 
that it was planned to feed the animal sufficient food to 
cause it to maintain a uniform body weight. As a matter 
of fact, the animal added somewhat to his total weight 
in the ten months of stunting. The tables and pictures 
(Plate XXV) give a very clear idea of the general results 
of this trial. The full-fed animal gained rapidly and at 
the end of fourteen months weighed 956 pounds. The 
young animal fed merely a maintenance ration weighed 

^ Missouri Experiment Station, unpublished data. 




Plate XXV. — Permanent effect of retarded growth. The animal on the 
left (No. 527) was fed the maximum amount of a nutritious ration from birth. 
The animal on the right (No. 529) was starved until twelve months of age 
and then fed generously to age thirty-eight months. See table on page 269. 



DEVELOPMENT 



269 



only 207 pounds at the age of thirteen months. At that 
time, the animal was emaciated in appearance, showed 
every symptom of starvation, and was to all appearances 
very severely stunted in its growth and development. 
From twelve months to thirty-eight months, the animal 
fed previously on a maintenance ration was later given a 
generous ration and gained during that period a total of 
1280 pounds. The full-fed animal during the same period 
gained 853 pounds. At the end of the period the animal 
that was stunted during its early life was over 300 pounds 
lighter, was apparently somewhat shorter, with finer bones, 
than the full-fed animal. There was little doubt but that 
in this trial the early environrnent permanently decreased 
the size of the adult animal. 

255. Early stunting and the capacity to grow. — It is 
interesting to know that the capacity to grow was not 

The Permanent Effects of Retarded Growth 

Feed and Weight Records of Two Steers for 24 Months ' 

No. 527 was fed a generous ration until 38 months of 
age. No. 529 was starved for the first 12 months and 
then given a full ration until 38 months of age. 



Initial Weight (lbs.) 
Final Weight (lbs.) 
Gain during Period 
Av. Daily Gain . 
Grain Fed Daily . 
Hay Fed Daily . . 
Grain per Lb. Gain 
Hay per Lb. of Gain 
Total Grain Eaten 
Total Hay Eaten . 



Age 1 TO 12 Mos. 



No. 527 No. 529 



165.0 

901.8 

736.8 
2.046 
6.926 
3.578 
3.384 
1.748 

2493.44 

1288.12 



175.0 

213.5 
38.5 
0.106 
0.571 
0.895 
5.343 
8.370 

205.73 

322.53 



Age 12 to 18 Mos. 



No. 527 No. 529 



901.8 
1178.2 
276.4 
1.535 
14.686 
6.401 
9.560 
4.168 
2643.48 
1152.18 



213.5 

694.9 

481.40 
2.674 
10.030 
4.840 
3.750 
1.813 
1805.50 

872.83 



Age 12 to 24 Mos. 



No. 527 No. 529 



901.8 
1401.7 
499.9 
1.388 
13.610 
5.821 
9.801 
4.191 
4899.86 
2095.58 



213.5 
1054.7 
841.2 
2.336 
11.829 
5.642 
5.062 
2.415 
4258.55 
2031.13 



270 



THE BREEDING OF ANIMALS 









J 








-ti 




J 




fl 

o 




s? 




d 


» 


o 




m 




^ 




CO 


O 


00 




o 


|T| 


«0 






o 


o 


CD 


T— 1 


p 

< 




CM 

O 

ft 


03 


H 


s^ 


a 


CD 


W 




o 


^ 


CC! 


s~ 


<t> 


4-3 


fa 


^ 


rO 


S 


o 


^ 


a 







o 




e*-! 






03 


fl 



fa 


> 


ai 


c3 


fa 


5~ 


1 


i:-! 




O 


fl 


H 


O 




«*-( 


1^ 


Q^ 




o3 




C3s 




T3 

«4-l 


1^ 

fin 






1— H 








1 


Eh 






•a 

e3 




f^ 







05 




>0 CD Tt^ '^ 10 







05 -^ t>. CO t^ lO 1-1 


§ 




ooqoO'-HC^c^r-.iOfNcD 


00 


»o 


iOt^<M"'-5oiTt^t>lcO^(N 


W 


Q 


t^ CO CD Tti t>. 





^ 


T-H to CO »0 00 


g 


rH^ q-tH 


i-l 




1— I 











CD CO GO CO ^ 


« 




lO ■* 10 CO 1— 1 c: 


^ 


iM 


Qqq^oq<NrHCDrHoo 


10 


lOLOCJi-Hi-HiOOOCOC^Tt^ 


W 


6 


CD (M CD T-i Oi 


>4 



1— 1 00 CD to Oi 


^r^ CO ^ 


^ 




1—1 






CD -^ Tti 10 Oi 


CO 


05 


Tti to CO »0 1-H !>. l> 


&4 


10 


TjHoq^(NcDi-;l>T-ji>T^ 


iz; 


cor^-^i-H-^tOi-H-rj^t^Tt^ 








1-H CO (N 1-1 r-t CO CM 


§ 


'^ 


CO to CM CD Oi 


CO 




1—1 1—1 CM 


CO 









-^ CO Oi 00 t^ 


t^ 


CD CO to 00 00 00 CO 






T^OOt^i-iOi-^TfiOiCD 




t^t6l>d^TfHo6cDCOCM 


< 


6 


00 CM CO tH 1-1 TtH Oi 


Z 


CD 00 '-H to 00 




1-1 i-H CM 






l:^ CO Tt< CD 






Oi to CO CO CM 00 




05 


tqooCOCDCMoqoO'^iOO 


10 


cor^-^r4coioi>c6toc5 


^ 


Q 


i-H CO CM r-i CO to 





^ 


CM to CO CO to 


S 


CM ^ (-J-'* 


00 




1—1 


CO 









CO 1> CO ^ 00 






00 1-1 CO CM Oi to 00 


IN 

1-H 


IN 


QOOCMi-JrHqOipi>;CD 




U5 


i-Ht6c0rHTi^CDi-5tO06cd 


P^ 






CM CM 1-1 1-1 00 


< 


^ 


Oi 00 Oi l> 

T— 1 






I5II • --IsSfl 












^ ^ ": g fl ^ fl ^— --3 






•^ g.S 5-^ >>-S >>i^ ii . 
5feO<10MOW^H 











DEVELOPMENT 271 

destroyed by the early stunting resulting from insuffi- 
cient food. The gains, the amount of food consumed, 
and the gain in live weight based on each pound of 
grain consumed is shown in the tables for the various 
periods of the feeding experiment. (Tables on pages 
269, 270.) It will be observed from the figures given 
in these tables that the animal subjected to severe condi- 
tions of feeding during its early life evidently had a 
greater capacity for growth, and made better use of the 
food consumed, than did the animal that received a 
generous ration during the same period of its life. 
There can be no question but that under certain con- 
ditions a significant check to the development of an 
animal may actually increase the rate of growth during 
the later periods of its life. 

256. Climate. — Small animals like mice and domestic 
rabbits reared in artificially heated temperatures are 
noticeably larger than normal size and have less hair on 
the bodies. Cattle that are well fed and housed in warm 
barns have much less hair than animals of similar breed- 
ing that are required to live exposed to the rigors of severe 
cold weather. 

257. The age factor in animal-breeding. — Very large 
numbers of farm animals are bred and produce offspring 
while still immature. The use of young sires among 
all classes of animals is general, but especially is their use 
common in the breeding of hogs, sheep and cattle. 
Various opinions exist among breeders as to the good or 
evil effects which follow this practice. Some of the evil 
results which it is claimed have followed the long-con- 
tinued mating of immature animals are, a gradual decrease 
in the size of the breed ; weakness of constitution ; loss 
of prepotency in the transmission of valuable qualities; 



272 THE BREEDING OF ANIMALS 

a retardation of the growth of the young parents and, in 
some cases, a permanent dwarfing of the mother. 

The supposed evil results following premature preg- 
nancy must result either from variations produced in the 
fundamental constitution of the germ-plasm or in changes 
in the soma- or body-cells. Those breeders who contend 
that long-continued breeding of immature animals results 
in actually decreasing the size of the race or breed believe 
that the real character of the breed has been changed, and 
changed in such a way that the individuals of the breed 
are no longer able to produce offspring which possess the 
capacity to develop into animals of the recognized stand- 
ard size of the breed. They would insist that the funda- 
mental nature of the breed has been changed in such a 
■vYay as permanently to affect their hereditary character. 
It is obvious that if this contention of breeders is correct, 
it is contrary to our present ideas of the inheritance of 
acquired characters. Biologists generally would first 
insist on a more accurate demonstration of the alleged 
fact that the size of the breed is actually diminished as a 
result of early pregnancy and lactation. If it should 
be found that this practice has apparently resulted in a 
smaller breed, the biologist would undertake to explain 
the observed fact on different grounds. 

258. Premature breeding decreases size. — First, is it 
true that premature breeding has ever resulted in decreas- 
ing the size of the breed? It must be admitted that 
experienced breeders are very often accurate observers. 
Investigators who disregard the facts which have been 
determined by practical breeders through a long period 
of successful experience are neglecting a valuable source 
of knowledge on many of the complex problems of heredity 
and development. That breeders have observed that long- 



DEVELOPMENT 273 

continued early breeding results in decreasing the size 
of the breed is indicated from an investigation made by 
J. M. Jones under the writer's direction in 1912. Spe- 
cific questions were formulated and sent to a large r umber 
of successful breeders in America and Great Britain. 
From these replies it was determined that 216 breeders 
had observed that early mating resulted in weakening 
the breed, diminishing the fecundity, and decreasing the 
size. That such results followed was denied by thirty-five 
breeders. Of the total number replying, 158 believed 
that the size was decreased but that fecundity was not 
diminished. It is very clear from the statistics presented 
and from the extended replies of the intelligent breeders 
that under certain conditions the size of the animals 
comprising the herd of a breeder who continually breeds 
his animals prematurely is smaller than the size of ani- 
mals in the herds of breeders who cause their animals to 
mate at a more mature age. 

259. Decreased size due to early breeding not in- 
herited. — In recognizing the fact that premature breeding 
does decrease the size of the breed under certain condi- 
tions, it is not necessary for us to assume that the tend- 
ency to decreased size in this case is inherited. Early 
breeding can have no direct influence in changing the 
fundamental constitution of the germ-plasm. It cannot, 
therefore, change the general prepotency of the breed 
in transmitting the recognized standard qualities of the 
race. We must therefore look for an explanation outside 
of the supposed influence on the hereditary powers of the 
breed. The real effects from premature mating are to 
be found in the development of the individuals as affected 
by environment. The effects of gestation and lactation, 
if observable at all, would be exhibited in the young par- 



274 THE BREEDING OF ANIMALS 

ents or their offspring, or in permanent effects on the race 
or breed. It might, in fact, influence all three. 

260. Influence of early pregnancy on the mother. — 
The chief harmful effect which follows the mating of 
immature breeding animals is a retardation Or sudden 
check to the growth of the young mother. Investigation 
shows that the premature exercise of the breeding func- 
tions in the young female acts in some instances as a 
temporary inhibitor of growth. The author has for six 
years compared the growth of immature mothers with the 
normal growth curves of mothers mated when more 
mature. In this investigation six Duroc Jersey sows were 
divided into three groups. These groups of two sows 
each were designated respectively as immature, half 
mature and mature. The sows of the immature group 
were bred at the beginning of puberty or at the first heat. 
At this early period the young mother was very imma- 
ture. The half mature sows were bred at about eighteen 
months and the mature sows at about thirty months of 
age. Careful records of the food consumed, the gain in 
live weight, and increase in body measurements were made 
of each animal in the experiment. Similar records were 
made of the female offspring of the original sows for sev- 
eral generations. The body measurements were taken 
with a view to determining muscular and skeletal increase. 
A large number of measurements was made, and these 
clearly demonstrated the fact that the early exercise of 
the breeding function in swine results in temporarily 
checking the growth of the mother. The investigations 
have progressed far enough at this time to measure also 
the ultimate effect upon the mature mother. While 
the observations have not yet included enough animals 
to justify us in speaking with finality, yet it seems entirely 



DEVELOPMENT 



275 



safe to conclude that under certain conditions premature 
breeding results in a permanent reduction in the normal 
size of the mother. Young sows which have been bred 
at the beginning of puberty and twice a year thereafter 
until full maturity have in every case been smaller at 
maturity than sows in the half mature and mature groups. 

Retardation of Growth Due to Premature Breeding 

OF Sows 

Measurements taken at 42 months of age 





Length of 
Body 


Heart 
Girth 


Height at 

Withers 


Depth of 
Chest 




Centimeters 


Centimeters 


Centimeters 


Centimeters 


Immatm-e^ . . . 


106 


125 


65 


41 


(Factor 6) 
Half Mature ^ . . 


124 


142 


70 


47 


(Factor 3) 
Mature^ .... 


116 


152 


71 


49 


(Factor 8) 











In the above table are recorded the more important 
measurements of a typical representative of each of the 
three groups. It will be observed that at forty-two months 
of age the immature sow was materially smaller in length 
of body, height at withers, depth of chest, and in heart 
girth. At this age (three-and-one-half years) the young 
sow had produced thirty-nine pigs in five litters, the half 
mature sow sixteen pigs in two litters, and the mature 
sow eight pigs in one litter. But one conclusion is possible 

1 Has produced 5 litters and a total of 39 pigs. 

2 Has produced 2 litters and a total of 16 pigs. 

3 Has produced 1 litter and a total of 8 pigs. 



276 



THE BREEDING OF ANIMALS 



from these results, that early pregnancy and lactation 
does retard the growth of the young mother. 

Retardation of Growth Due to Premature 
Breeding 

Measurements taken at maturity — 66 months of age 





Length of 


Heabt 


Weight at 


Depth of 




Body 


Girth 


Withers 


Chest 




Centimeters 


Centimeters 


Centimeters 


Centimeters 


Immature^ . . . 


108 


123 


66 


40 


(Factor 6) 










Half Mature 2 . . 


120 


127 


67 


44 


(Factor 3) 










Mature^ .... 


118 


143 


71 


48 


(Factor 8) 











In the above table the measurements of the same 
animals at full maturity are shown. At the time these 
measurements were taken the parents were about five-and- 
one-half years of age. The sow that was mated at the be- 
ginning of puberty and bred regularly thereafter, produc- 
ing sixty-nine pigs in nine litters, was smaller at maturity 
than either of the other groups which were mated at an 
older age. This result has been secured in a number of 
similar cases. In other words, the breeding of sows at a 
young age not only results in a temporary check to their 
development, but tends permanently to decrease the size. 
This permanent decrease is not very marked and practi- 
cally may not be of great importance. It is clear from the 



1 Has produced 9 litters and a total of 69 pigs. 

2 Has produced 6 litters and a total of 49 pigs. 

3 Has produced 5 litters and a total of 32 pigs. 



DEVELOPMENT 277 

records that one important practical result of early mating 
is that by following this practice a much larger number 
of young are produced during the lifetime of the parent. 
In producing hogs commercially, this advantage might 
easily overcome any disadvantage arising from a reduc- 
tion in the size of the mother. 

261. Gestation and lactation in relation to growth. — 
The two most important phenomena associated with 
reproduction which might have a measurable influence on 
growth are gestation and lactation. The period of gesta- 
tion in the mammalian domestic animals is the period dur- 
ing which the embryo is developing in the uterus, from 
the fertilization of the egg until the young animal is 
sufficiently matured to carry on an independent existence 
outside the body of the mother. During this period the 
unborn animal increases rapidly in size, and within its 
tissues the processes of cell division, absorption and 
assimilation proceed with exceptional energy. The nutri- 
tion for the growth of the foetus during this period is 
supplied entirely by the pregnant mother. The foetus 
itself has no means of nourishing its own tissues. It is 
wholly dependent upon the mother. To all intents 
and purposes the young animal in the uterus is an organic 
part of the body of the mother. The foetus is an enormous 
parasite nourished by the mother through the circulation. 

It is a popular opinion among many breeders that 
gestation is an exhaustive period for the mother, that 
during this period the mother must not only provide for 
her own physiological needs, but in addition must supply 
the materials needed for the rapid development of the 
foetus. It has been generally believed that because of 
these facts the period of gestation is a severe strain on the 
pregnant mother. If the mother herself has completed 



278 THE BREEDING OF ANIMALS 

her growth or has approached maturity in her develop- 
ment, the changes which take place in her organization 
and which may be due to her pregnant condition will 
obviously not affect her growth. On the other hand, if 
the mother is young and growing rapidly, gestation 
might act as a check to growth if the physiological pro- 
cesses of the mother are necessarily and chiefly directed 
toward the development of the foetus. The physiological 
processes concerned in the nutrition of the foetus are 
somewhat complex and the interrelations between the 
mother and her unborn young not completely deter- 
mined. The information available on the subject does 
not specifically answer the question. We know that the 
absorption of fats from the intestine proceeds at a more 
rapid rate during pregnancy. Increased amounts of fat 
in the liver cells also are associated with pregnancy. 

There is a tendency to increase in body weight during 
gestation. The maternal body increases in weight 
independently of the increase in size of the foetus and 
foetal membranes as shown by Gassner ^ and confirmed 
by others. This increase in weight is common to the 
mature pregnant mammalian mother and is not confined 
to the young parent only. It is possible, therefore, that 
this increase might be due to increased fat in the body 
and not to any increase in the skeleton. If this were 
found to be true, it would tend to confirm current opinion 
as to the retarding influence of gestation on the growth. 

262. The Missouri experiments. — At the Missouri 
Experiment Station ^ careful measurements have been 
made of a large number of immature pregnant sows and 

1 Marshall, "Physiology of Reproduction," chap. XI. 
- Mumford, Bulletins 131 and 141, Missouri Experiment 
Station. 



DEVELOPMENT 279 

of sows not pregnant for the purpose of answering, if 
possible, the question whether gestation is a period of 
such severe physiological strain on the young mother 
that it stops normal growth. A large number of animals 
have been under observation in this experiment and the 
results are fairly uniform. Measurements included rec-* 
ords of changes in body weight, heart girth, length of 
body, height at withers, and other measurements. 

The investigation is not complete, and further work 
may modify the conclusions which seem fully warranted 
at this time. The results so far justify the following 
conclusions : 

1. The exercise of the reproductive functions, con- 
tinuously from the beginning of puberty to full maturity, 
permanently decreases the normal adult size of the mother. 

2. This permanent effect on the size of the mother 
occurs even under a favorable environment. 

3. The period of gestation is not a check to growth 
when a full ration of nutritious food is supplied. The 
rate of growth is not lessened during gestation. There 
is some evidence that pregnancy is an actual stimulus to 
growth. 

4. The period of lactation is a very severe physiological 
strain on the young mother, and during this period growth 
is apparently inhibited. 

5. After the end of lactation or when the young are 
weaned, the rate of growth in the young mother is more 
rapid than before pregnancy and more rapid than in 
animals which have not been pregnant. 



CHAPTER XIV 
THE PRACTICE OF BREEDING 

If the modern breeds of domestic animals are com- 
pared with the original unimproved forms, remarkable 
differences will be observed. In many of the characters 
which have come to be of inestimable value to man, the 
modern animal is notably superior to the original unim- 
proved forms. And in other characters, less substantial 
and economically significant, modifications of great scien- 
tific interest have resulted from systematic selection by 
man. 

263. Improvement in size. — For many purposes the 
wild unimproved forms of the domestic animals are too 
small to accomplish successfully the work required by 
man. This demand for greater size and generally pro- 
portional increase in strength has led breeders consciously 
to select animals for size. The results of this selection 
may be observed in the gigantic modern draft horse. 
It is probable that all modern breeds of horses have 
developed from the same original type. The wild form 
was small in size, rough and somewhat angular in appear- 
ance, with short mane and scanty tail. From this animal 
we have through selection succeeded in producing the 
large, powerful draft horse with smooth, broad contours 
and heavy mane and tail. Contrasted with this type 
we have well-recognized pony types weighing less than 
400 pounds. Both types undoubtedly descend from the 

280 



THE PRACTICE OF BREEDING 281 

same prehistoric form. Each type breeds true. The 
chief distinguishing character of size is firmly fixed in the 
germ-plasm and we must come to the conclusion that 
these radical differences have resulted from selection and 
have become firmly established hereditary characters. 
Similar differences in size among cattle, sheep and swine 
supply additional evidence that size is a character which 
may be radically changed through selection and that this 
variation may become so firmly fixed that it may be re- 
garded as an established characteristic of the breed. 

264. Improvement in function. — The most remark- 
able achievements in the improvement of the domestic 
animals are undoubtedly improvements in the various 
physiological functions of the animals useful to man. 
Some of the most noteworthy of these are the milking 
function in cattle, wool production in sheep, tendency 
to fatten in meat animals, speed in horses and egg-laying 
in the domestic fowls. A comparison of the productivity 
of each of these types of animals with the unimproved 
types gives ample evidence of the remarkable develop- 
ment which has taken place through the agency of man's 
selection. 

265. The milking function. — The ability of mam- 
malian animals to produce milk is closely correlated with 
the reproductive functions. The mammary glands func- 
tion primarily for the purpose of supplying a nutritious 
and easily digested food for very young animals. Among 
wild forms this function persists only for a comparatively 
brief period and its continuance is determined by the 
needs of the young mammal. Under domestication the 
milking function in the domestic cow represents a re- 
markable improvement. The wild cow probably sup- 
plied milk to her offspring only four or five months. The 



282 THE BREEDING OF ANIMALS 

amount of milk supplied by the wild cow is limited to a 
few pounds daily. 

The milking function in the domestic cow has become 
through man's selection an hereditary character of the 
greatest importance. While in the domestic cow the 
milking function is still closely correlated with the repro- 
ductive functions, it is nevertheless developed to such 
an extent that it bears no very important relation to the 
needs of the young offspring. Certain individual cows 
have this function developed to such an extraordinary 
degree that they produce milk continuously without inter- 
ruption for many years and often regardless of whether the 
cow becomes pregnant or not. (Plate XXVI.) 

The Holstein Friesian cow, Duchess Skylark Ormsby 
(Plate XXVII), produced 27,761 pounds of milk in one 
year, containing 1205 pounds of fat. The Jersey cow, 
Sophie 19th of Hood Farm (Plate XXVIII), has a record 
of 17,557 pounds of milk containing 999 pounds of fat. 
The Guernsey cow, Murne Cowan, is officially reported as 
having produced 24,008 pounds of milk and 1098 pounds 
of butter-fat in one year. Garclaugh May Mischief, an 
Ayrshire cow, has a similar yearly record of 25,329 
pounds of milk and 894 pounds of fat. 

266. Improvement in wool production. — The first 
importations of Spanish Merino sheep into the United 
States were made about 1815. At that time the average 
weight of fleece was three or four pounds. The weight 
of fleeces of American Merinos increased gradually from 
that time until 1885. Authentic records of single fleeces 
weighing from thirty to forty pounds are now available. 
The Oklahoma Agricultural College has reported that 
the two-year-old Rambouillet ram Loraine owned by 
that institution has produced a fleece weighing 46 pounds 



THE PRACTICE OF BREEDING 283 

which is claimed to be the heaviest fleece ever taken from 
a single sheep. The staple of this fleece was three and 
one-fourth inches in length, which when straightened 
measured five inches. It is interesting to note in this 
case that the fiber was of unusual fineness, averaging 
Yg^Q- of an inch in diameter. - According to Hunt,^ the 
average weight of fleece of all sheep in the United States 
in 1850 was 2.4 pounds a head. In 1900 the average 
weight of fleece was 6.9 pounds a head. This remarkable 
development in the improvement of the wool-producing 
qualities of animals must be wholly credited to the skill 
and enterprise of the American shepherd. 

267. Improvement in tendency to lay on fat. — It is 
more difficult to give accurate statistics showing the 
improvement in meat-producing animals. At the begin- 
ning of the eighteenth century, fat animals were not 
placed on the market until they were four or five years of 
age. Even as late as 1875, three- and four-year-old fat 
animals were the most common types of cattle to be found 
in the fat stock markets of America. By careful selec- 
tion the tendency to lay on fat has been developed in 
animals to such an extent that now it is common to find 
young animals carrying fat equal to that shown by four- 
and five-year-old bullocks of earlier years. This tend- 
ency to lay on fat at an early age is transmitted through 
heredity. The amount of food required to make one 
pound of gain is much less in the younger animals and 
the improvement in this respect, therefore, is of great 
economic significance. It requires less food to-day to 
produce the fat beef, pork and mutton sold in the markets 
of the World than was the case before the improvement 
of this tendency to early maturity. (Plates XXXI and 
XXXII.) 

^ Hunt, " Cyclopedia of American Agriculture," vol. 3. 



284 THE BREEDING OF ANIMALS 

268. Improvement in speed. — The ability to go fast 
at the trot is a development of American horse-breeding 
enterprise. The first trotting race was held at Boston 
in 1815. The fastest time made in this race was a mile 
in three minutes. As the result of interest in trotting 
races and the invention of light horse-drawn vehicles, 
the demand for speed at the trot resulted in great improve- 
ment in this direction. The record time of trotting horses 
decreased from year to year until at the present day (1916) 
several horses have been developed that are able to trot 
a mile in less than two minutes. The examples men- 
tioned are all noteworthy as examples of man's power to 
change fundamentally the form and function of the 
domestic animal. These examples could be indefinitely 
multiplied. 

269. Selection. — All wild forms that have been do- 
mesticated possess characters of economic value to man. 
They were domesticated for that reason. These valuable 
qualities have been, in many cases, greatly improved 
through the agency of man. So great has been the im- 
provement in many animal forms that the domesticated 
animal is markedly different from his wild ancestors. 
Many varieties, races or breeds exist and each of these 
differs in important particulars not only from its wild 
relatives but from all other varieties having similar ances- 
tral history. 

How have these valuable characteristics come into 
existence? What natural laws have guided man in the 
improvement of animals? Are the valuable character- 
istics of animals due chiefly to inheritance or are they in 
most part the result of improved conditions which sur- 
round the domestic animals? Is it possible for us from 
a study of the history of the achievements of animal- 



THE PRACTICE OF BREEDING 285 

breeders to establish a guide to future practice in the 
improvement of animals? Answers to these questions 
not only have great value to practical breeders but have 
profound biological significance. 

270. Natural selection. — The theory of natural selec- 
tion which has so long influenced and determined the 
trend of zoological thought is an attempt to explain how 
the qualities of animals in nature have come to be. 
Through natural selection organic beings tend to adapt 
themselves to their surroundings. The more nearly 
the qualities of animals are favorable to a successful 
existence under the conditions surrounding the individual, 
the more certainly will the animal live and reproduce. 

The insect that rests upon the branches of trees will 
escape insectivorous birds more certainly if the color of 
the body imitates that of the bark upon which it rests. 
The color of the jungle animal blends so completely into 
the general landscape that its presence is not detected 
by its enemies. 

The shore birds or waders in their pursuit of food in the 
shallow waters of the shore have developed long legs. The 
giraffe, feeding as it does upon the leaves on the branches 
of trees, has found a long neck to be a desirable quality in 
securing food. And in this case the longer the neck the 
more certainly will the animal survive when food is scarce. 

Darwin assumed that under conditions similar to those 
mentioned, animals that vary slightly in the desired 
direction would be preserved and would reproduce, while 
those animals that varied away from the valuable quality 
would perish. An animal might continue to develop 
indefinitely in a given direction through continuous 
variation. Darwin also recognized the existence of 
discontinuous variation. 



286 THE BREEDING OF ANIMALS 

The origin of the pecuHar characters which are valuable 
in the domesticated animal is believed to have come 
about through a similar process of selection but with this 
difference : Man has introduced methodical selection by 
which all animals are preserved, not only those suited 
to their particular environment but also and chiefly those 
which possess characteristics that are valuable to man. 
Many complex and difficult questions have arisen in con- 
nection with the improvement of the domesticated ani- 
mals involving the most difficult problems of inheritance. 

271. Methodical selection. — The selection practiced 
by man is known as methodical selection. Animals are 
selected because of their peculiar fitness for special pur- 
poses. The powerful, heavy draft-horse is the result of 
generations of careful selection and breeding in an effort 
to produce an animal that can pull heavy loads. 

In the same way but with a different standard of selec- 
tion, the speed horse has developed an extraordinary 
ability to run fast under the saddle or trot at a rapid pace 
before the carriage. 

Similarly, the beef animal, the dairy cow, the mutton 
and wool sheep, the lard and bacon hog, the swift grey- 
hound, the massive St. Bernard, the intelligent Scotch 
collie and many other types useful to man have come 
from methodical selection. 

272. Importance of selection in animal-breeding. — 
Careful study of the methods which have been practiced 
by breeders of the domestic animals cannot fail to lead 
to the inevitable conclusion that selection has been the 
most important if not the chief principle followed in bring- 
ing about the present highly developed forms among 
animals. 

Certainly not all the phenomena which are exhibited 




Plate XXIX, — Daughters of the same sire, illustrating great uniformity 
in conformation and productive power resulting from the use of a prepotent 
sire in the herd. These three cows have an average yearly record of 22,295 
pounds of milk and 855 pounds of butter. Owner, University of Missouri, 




^/^JJ^S 








Plate XXX. — Three generations showing impressive character of 
original dam. Upper, Missouri Chief Josephine, yearly milk record 26,861 
pounds. Middle, Missouri Josephine Sarcastic, daughter, yearly milk record 
18,452 pounds. Lower, Carlotta Campus Girl, granddaughter, yearly milk 
record 15,725 pounds as a two-year-old. Owner, Universitj' of Missouri. 



THE PRACTICE OF BREEDING 287 

in the practices and results of animal-breeders can be 
explained upon the basis of selection alone, but it is quite 
certain that without selection little practical use could 
be made of the known laws which govern the transmission 
of characters. Man's chief agency in the improvement 
of animals has not been a conscious effort to bring about 
a series of variations or mutations of a certain kind, but 
it has rather been in the direction of preserving such 
valuable characteristics as have been already in existence 
or have appeared through variation. These character- 
istics have been intensified by judicious matings and 
perpetuated as a result of the keen insight of the skillful 
breeder. The successful breeder has ever in mind an 
ideal. He is at all times alert to detect variations which 
approach this ideal. 

Darwin believed that most of the improvement wrought 
in domestic animals was due to minute or continuous 
variations from the less desirable to the more desirable. 
This belief has been general among animal-breeders 
themselves. Working upon this assumption, the work of 
the breeder consisted merely in accurately observing the 
variations which tended in the desired direction. 

But continuous variation assumes a perfect series of 
infinitesimal steps, each grading into the one higher or 
lower. Such continuity exists in the growth of animals 
from birth to maximum development. Continuous varia- 
tion is also illustrated in the physical world by changes 
in temperature. In the history of the improvement of 
domestic animals there are many examples of marked 
and sudden variations in the offspring which cannot 
be continuous. Such variations have been called dis- 
continuous variations or mutations. It is certain that 
much of the improvement in the domestic animals has 



288 THE BREEDING OF ANIMALS 

come from valuable mutations which have been recognized 
by the alert breeder. 

But whether the present valuable characteristics of 
the domestic animals have come through continuous 
variations or by sudden mutations or in any other way, 
selection by man has been the one outstanding fact in 
the development of the many valuable races and breeds 
of animals. It is conceivable and very probable that 
similar variations have been induced by similar causes 
in all wild forms, but wild forms have remained relatively 
stationery while the domestic races have been greatly 
improved. 

273. Aids to selection. — The breeder has consciously 
or unconsciously brought to his aid numerous practices 
which have greatly facilitated his efforts. The manu- 
facturer who has invented a labor-saving device or a 
complicated machine to perform certain work puts it to 
the test by actually applying the machine to the work 
in hand. Likewise the skillful breeder has found it greatly 
to his advantage to test his animal creations by actual 
performances. 

The breeders of trotting horses have no means of deter- 
mining how successful they are in producing speed except 
by trial on the track and it is not only necessary to train 
now and then a horse but every individual in the stud 
must be tested to be certain that all possess the quality 
of speed. 

The highly successful breeders of meat animals, cattle, 
sheep and swine, maintain their breeding animals in a 
high state of condition. In some cases the meat animals 
used for breeding purposes by noted breeders are kept 
so fat as to interfere with the normal reproductive func- 
tions. But even so, such a practice is essential to the 



THE PRACTICE OF BREEDING 289 

skillful breeder because in no other way can he determine 
whether or not his breeding animals themselves possess 
the proper tendency to lay on fat which is an essential 
characteristic of a well-improved meat animal. 

A high condition of the breeding animals does not 
in any sense give the beef animal a greater power to trans- 
mit the tendency to lay on fat to the offspring, as some 
breeders have believed, but it does give him a selective 
device or measure by which he may always know whether 
his breeding animals themselves possess the characters 
which it is desired to transmit to the offspring. 

The breeders of dairy cattle feed their cows to full 
capacity and surround them with every favorable condi- 
tion for the maximum production of milk. This practice 
gives the breeder the only accurate measure of individual 
performance and places in his hand a selective device by 
means of which he can quickly eliminate from his herd 
those animals that have not inherited the capacity for 
high production. There is no other accurate measure- 
ment which the breeder can employ that will certainly 
register his progress in the improvement of his favorite 
breed. 

274. The real results of selection in the improvement 
of the domestic animals. — The many improved breeds 
of live-stock which are now possessed of qualities of great 
economic value to man, have come to this possession 
through artificial selection practiced by man. Are these 
qualities which distinguish the improved breed from the 
wild form a permanent possession of the race? Have 
the selective processes applied by man resulted in so fixing 
the desirable heritable characteristics that the breeder 
may depend upon inheritance to repeat the characters 
of the parents in the offspring? There are some indi- 
u 



290 THE BREEDING OF ANIMALS 

viduals in each breed that represent near perfection in 
the development of characters. There are many others 
that are more or less deficient in such characters while 
other individuals are actually mediocre. Will the indi- 
vidual with near perfect characters reproduce other 
individuals of the same high quality ? Will the mediocre 
sort beget like mediocrity ? In other words, are the quali- 
ties which have resulted from artificial selection indelibly 
impressed on the hereditary substance of the germ-plasm 
in such a way as to be certainly transmitted to the off- 
spring? Exact answers to these questions cannot be 
given without full knowledge of all the conditions, but 
recent investigations have thrown much light on these 
important questions. 

275. Selection within pure lines. — Selection as prac- 
ticed by man has undoubtedly resulted in marked im- 
provement of the domestic animals. This improvement 
is apparently transmitted, or at least it is possible by 
continued selection to reproduce desirable characteristics. 
By continually selecting individual breeding animals 
which show a tendency to vary in the direction desired, 
it has been assumed that the race or breed would gradu- 
ally move in the direction of selection. 

At one period in the history of Shorthorn cattle, all 
breeders were agreed that their improvement was mainly 
to be accomplished in the direction of increased size. 
Consequently the animals of greatest scale were selected 
and mated with the apparent result that the average size 
of the breed was increased. But actually what was 
accomplished after many generations of selection? Was 
a new breed created ? Had selection acted as a causa- 
tive principle? The teachings of Darwin and his fol- 
lowers has undoubtedly resulted in creating the impres- 



THE PRACTICE OF BREEDING 291 

sion among many students that in this case a new breed 
had actually been created with new characters resulting 
from selection of continuous variations. That the results 
obtained in this and similar examples may l:e explained 
on other and more probable grounds has been clearly 
demonstrated by Johannsen.^ This Danish botanist 
working with garden beans found that the whole popula- 
tion is made up of many races which he called " pure 
lines." Selecting from populations composed of pure 
lines, the breeder merely sorts out one of these races 
and in time secures a pure line. This pure line or race 
is not new. It has not resulted from gradual or continu- 
ous variations but has simply been separated out from 
a number of others. According to Johannsen, selec- 
tion within a pure line during a number of generations 
had no effect in improving the variety. The germ- 
plasm of all individuals of a pure line tends to become 
homogeneous. 

The mating of individuals from a pure line having 
in their respective germ-plasms identical factors will 
result in producing identical offspring and hence any 
amount of selection will prove futile. Such pure line 
individuals are much more likely to be found among plants 
than among animals. Plants that are self-fertilizing may 
be expected to develop typical pure lines and selection 
within such pure lines will be of no avail. Among the 
higher animals similar results undoubtedly occur, but 
the difficulties of securing a strictly pure line are very 
much greater owing to the necessity of mating two dis- 
tinct individuals whose ancestry, while similar, cannot 
possibly from the very nature of the case, be exactly 
identical. 
1 Johannsen, "Elemente der exakten Erblichkeitslehre," 1909. 



292 THE BREEDING OF ANIMALS 

276. Vilmorin's pure line wheat-breeding. — A good 
example of the pure line theory among plants is to be 
found in the very practical and meritorious work of 
Louis de Vilmorin, who began the improvement of com- 
mercial varieties of wheat in France about 1840. Vil- 
morin carefully selected a single head of outstanding merit 
and from this by in-breeding established a pure line or 
variety which has bred true to the original ear or head. 
The commercial seed offered by Vilmorin was always 
descended from a single plant. Selection in this case 
failed to bring about any improvement over the original 
plant, as shown by the Hagadoorns.^ 

"In 1911 Mr. Meunissier, the genetist of the firm of 
Vilmorin, found the collection of original ears of the varie- 
ties with which Louis de Vilmorin half a century back 
began his living museum. Some of these wheats are 
from the harvest of 1843, others date from 1850, or inter- 
mediate dates. Mr. Meunissier chose three dozen ears 
of varieties which are still in the collection, and which 
have therefore been bred continuously as pure lines for 
about fifty years. We compared these ears to ears of 
the 1911 harvest, and photographed them side by side. 
Some of these pairs of ears are here shown, each pair con- 
sisting of the old ear, and its descendant, half a century 
later. All these generations of selection have not changed 
any one of the varieties one little bit. It can therefore 
safely be concluded from this series of experiments, that 
selection can have no effect in material pure for its 
genetic factors. Genetic factors are constant." 

277. Selection most useful when genetic factors are 
not pure. — The pure line theorj^ explains why any 

1 Mrs. C. and Dr. A. L. Hagadoorn, "Selection in Pure Lines," 
American Breeder^s Magazine, 1913, p. 165. 



THE PRACTICE OF BREEDING 293 

improvement among the best strains of animals is so 
diflficult. Highly improved breeds or families among 
the domestic animals have reached a degree of purity 
wherein the germ-plasm represents an approach to homo- 
geneity. When such a pure line has been established, 
the old adage that " like begets like " becomes a really 
working principle and a guide to practice. The novice 
need not expect to accomplish great improvement in the 
highly developed breeds of live-stock. The greatest 
improvement will be made in breeds or strains of mixed 
breeding, genetically speaking. 

The improvement of animals of mixed character which 
will result from the efforts of a breeder is probably to be 
explained as a gradual separation of the desirable pure 
lines and mating the individuals which possess these 
characters. This results in time in the establishment of 
a strain or breed which is prepotent in transmitting the 
desired qualities when after many generations of pure 
line breeding this strain has reached a point where the 
germ-plasm of the breeding animals is pure in respect 
to its genetic factors ; then any considerable improvement 
will be no longer possible. 

278. Pure line theory not opposed to improvement by 
selection. — The practical breeder whose experience has 
demonstrated clearly that improvement among the regis- 
tered or '^ pure-bred " races of the domestic animals has 
followed careful and persistent selection will hesitate 
to accept the statement of Johannsen and his followers 
that " selection within the pure line is without effect." 
But the improved breeds of live-stock, however pure 
in breeding, are not to be regarded as fulfilling the require- 
ments of a " pure line " in the biological sense. The 
breeds of live-stock are yet far from homogeneous in 



294 THE BREEDING OF ANIMALS 

the sense that they have been selected to a point where 
the germ-plasm of different individuals of the breed, is 
identical in composition. The pure line of the biologist 
is after all a purely imaginary conception. It is conceiv- 
able that such a condition may be produced among self- 
fertilizing plants, but among the higher animals it is 
certainly true that no such germinal purity has yet been 
attained. The practical animal-breeder may still con- 
tinue to hold fast to selection as his chief means of im- 
provement with the assurance that in all the higher do- 
mestic animals we have not yet reached the ultimate 
limits of improvement. The animal-breeder has not 
yet produced a pure line, biologically speaking, and has 
not, therefore, reached a point in his breeding when it 
can be accurately said that selection is without effect.^ 

279. Pedigree. — The pedigree of an animal is a record 
of the ancestors. It is a valuable historical document. 
If it includes the names of many animals of outstanding 
quality, it is a good pedigree. If the ancestors were 
mediocre individuals of no special merit, the pedigree 
is inferior. The mere fact that an animal is recorded in 
a recognized herd-book does not signify that such animal 
has a good pedigree. The careful breeder must have a 
thorough knowledge of the history of the breed and espe- 
cially of the ancestors of the individual animal under 
examination. 

The immediate ancestors are most important. A 
noted sire or dam appearing in the pedigree six or eight 
generations back is of far less importance than one which 
appears in the first, second or third generations. Many 
breeding animals are sold on the strength of the fact 

* Castle, "Pure Lines and Selection," Journal of Heredity, 
1914, p. 93. 




HI A^ 1 


& ■ *^ ''^^^ 


fi^^^^lP^jd^^B^ .^^:4s«HJi 


^^I^Mp 




^^"^11 




#r--' - -^ 


1 


.*?«S*«s#:-- 


Pi 


.;"-■ 


n| 


JM^iiT^iiffl 


'iwitti^ JHH^nH 






THE PRACTICE OF BREEDING 295 

that they are descended from some famous sire or dam 
ten or even twenty generations back. If Galton's law 
of ancestral heredity is a fair estimate of the potential 
strength of a breeding animal, we should expect that 
the individual animal would inherit one-half from his 
two immediate parents, one-fourth from his four grand- 
parents, and one-eighth from his eight great-grandparents. 
From one great-grandparent, therefore, we should expect 
the inheritance in the descendant to be represented by 
the fraction g^. It is evident that a single ancestor six 
or eight generations removed would contribute a very 
small fraction of the sum total of qualities of the individual. 
In the application of Galton's principle, it is necessary 
to assume that all the ancestors are equally prepotent. 
This assumption is contrary to the experience of breeders. 
Certain individuals are known to be more prepotent 
in certain characters, or, more properly speaking, certain 
characters are dominant and others recessive. The 
dominant characters will largely determine the character 
of the offspring. It is conceivable that a dominant char- 
acter which it is greatly desired to perpetuate in a strain 
might reappear in the offspring through many genera- 
tions. It might be argued that because of this fact a 
study of the characters of an ancestor far removed hav- 
ing this character would be valuable. To this it must 
be said that if the character is dominant it will be clearly 
apparent in the immediate ancestors. If it is not apparent 
it may have been lost or overshadowed by the develop- 
ment of other characters, and if so it is good evidence that 
the real character of the strain is being determined by 
nearer and stronger ancestors. Every modern biological 
conception gives added weight to the principle that it is 
the recent ancestors that should be most carefully in- 



296 THE BREEDING OF ANIMALS 

vestigated by the practical breeder if he is to obtain any 
valuable basis for estimating the breeding powers of an 
individual. 

280. Registered breeding animals. — In purchasing 
a breeding animal, the breeder desires some guarantee 
of purity of breeding. Every recognized breed, therefore, 
maintains an association of breeders organized for the 
purpose of safeguarding the purity of the breeding ani- 
mals and advancing the general interests of the breed. 
Each association maintains a record book in which every 
animal recognized as a pure-bred animal of the breed is 
recorded. Each association has its own rules governing 
the registration of animals. In practically all breed 
associations, the offspring of registered parents can be 
recorded. There are few exceptions to this rule. In 
some associations animals may be registered upon the 
basis of their performance. The Standard Bred or 
American Trotting Horse Registry Association will record 
any animal that has made an authentic record of a 
mile in two minutes and thirty seconds on an approved 
track and under regulation rules. A few associations in 
the past have permitted the registration of animals hav- 
ing a certain number of top crosses to registered sires. 
The history of all breed associations is similar. A few 
animals of similar characters have attracted attention 
because of their peculiar value for certain purposes. 
These animals have been interbred and gradually a family 
or strain developed which excels in certain valuable 
characteristics. The admirers of this family or strain 
have organized to preserve the strain. Experience has 
shown that one of the first and most useful steps is to 
record the individual breeding animals of outstanding 
merit. The descendants of these animals constitute 



THE PRACTICE OF BREEDING 297 

the breed, and ultimately only descendants of animals 
recorded in the registry book are eligible to registration. 
281. Registry associations. — The recognized registry 
associations of the United States at present (1916) are 
listed below : ^ 

AMERICAN HORSE RECORD ASSOCIATIONS 

Arabian Horse Club of America. 

American Association of Importers and Breeders of Belgian 

Draft Horses. 
Cleveland Bay Society of America. 
American Clydesdale Association. 
French Coach Horse Society of America. 
National French Draft Horse Association of America. 
German, Hanoverian and Oldenburg Coach Horse Association 

of America. 
American Hackney Horse Society. 
American Morgan Register Association. 
Percheron Society of America. 
The American Breeders' and Importers' Percheron Registry 

Company. 
American Saddle Horse Breeders' Association. 
American Shetland Pony Club. 
American Shire Horse Association. 
American Suffolk Horse Association. 
American Trotting Register Association. 
The Jockey Club. 
The Welsh Pony and Cob Society of America. 

AMERICAN JACKS AND JENNET RECORD 
ASSOCIATIONS 

American B.reeders' Association of Jacks and Jennets. 
Standard Jack and Jennet Registry of America. 

AMERICAN CATTLE RECORD ASSOCIATIONS 

American Aberdeen-Angus Breeders' Association. 

Ayrshire Breeders' Association. 

Brown Swiss Cattle Breeders' Association. 

1 Data from United^ States Department of Agriculture. 



298 THE BREEDING OF ANIMALS 

American Devon Cattle Club. 

Dutch Belted Cattle Association of America. 

American Galloway Breeders' Association. 

American Guernsey Cattle Club. 

American Hereford Cattle Breeders' Association. 

Holstein-Friesian Association of America. 

American Jersey Cattle Club. 

American Kerry and Dexter Cattle Club. 

Polled Durham Breeders' Association. 

American Polled Hereford Breeders' Association. 

Red Polled Cattle Club of America, Inc. 

American Shorthorn Breeders' Association. 

American Dairy Shorthorn Cattle Club. 



AMERICAN SHEEP RECORD ASSOCIATIONS 

American Cheviot Sheep Society. 

American Cotswold Registry Association. 

The Continental Dorset Club. 

American Hampshire Sheep Association. 

American Leicester Breeders' Association. 

National Lincoln Sheep Breeders' Association. 

American and Delaine Merino Record Association. 

Dickinson Merino Sheep Record Company. 

National Delaine Merino Sheep Breeders' Association of Wash- 
ington County. 

Standard Delaine Merino Sheep Breeders' Association. 

American Rambouillet Sheep Breeders' Association. 

International Von Homeyer Rambouillet Club. 

Michigan Merino Sheep Breeders' Association. 

Vermont, New York, and Ohio Merino Sheep Breeders' Asso- 
ciation. 

American Oxford Down Record Association. 

American Romney Marsh Breeders' Association. 

American Shropshire Registry Association. 

American Southdown Breeders' Association. 

American Tunis Sheep Breeders' Association. 



GOATS 

American Angora Goat Breeders' Association. 
American Milch Goat Record Association. 



THE PRACTICE OF BREEDING 299 

AMERICAN SWINE RECORD ASSOCIATIONS 

American Berkshire Association. 

American Large Black Pig Society. 

Cheshire Swine Breeders' Association. 

O. I. C. Swine Breeders' Association. 

Chester White Record Association. 

American Duroc Jersey Swine Breeders' Association. 

National Duroc Jersey Record Association. 

American Hampshire Swine Record Association. 

American Poland China Record Company. 

National Poland China Record Company. 

Standard Poland China Record Association.^ 

American Tamworth Swine Record Association. 

American Yorkshire Club. 

National Mule-foot Hog Association. 

Mule-foot Hog Breeders' Association. 

American Mule-foot Hog Record Company. 

282. Community breeding. — The establishment and 
maintenance of a recognized breed is a cooperative enter- 
prise. No single individual can alone successfully estab- 
lish and maintain a breed. Other things being equal, 
the larger the number of breeders engaged in the improve- 
ment of a given breed, the more certainly will the breed 
be improved and established on a permanent foundation. 
It is also true that it is distinctly to the advantage of a 
breed to be owned by breeders living in the same region. 
The interests of the breeders are greatly enhanced if 
many workers in a restricted area are breeding the same 
class of animals. This is particularly true in the case of 
the person who maintains a small herd or flock. The 
economic value of establishing for a community the repu- 
tation of breeding a very large number of a certain breed 
has been demonstrated in many localities in this and 
other countries. Recognizing these advantages, educa- 
tional organizations and breed associations have encour- 
aged community breeding enterprises. In some localities 



300 THE BREEDING OF ANIMALS 

this has taken the form of cooperation among three or 
four small breeders in the purchase of a valuable bull. 
In the United States many associations have been formed 
among farmers for the purchase of a valuable stallion. 
Even in the absence of conscious cooperation for improve- 
ment, if a large number of the farmers in a given neigh- 
borhood are like-minded in the selection of breeds and 
all produce the same breeds, each particular animal will 
actually be more valuable because prospective buyers 
will be attracted by the opportunity for selection where 
large numbers are available. 

283. Importance of numbers. — The present high 
quality of the highly improved and valuable breeds of the 
domestic animals has been the result of long-continued 
and rigid selection. The perpetuation of the improved 
characters already obtained rests upon the opportunity 
for continued selection of the same kind. The effective- 
ness of selection will depend upon the number of individual 
animals which are concerned in any given breeding proj- 
ect. It follows, therefore, that the breeder who produces 
large numbers has a decided advantage over the one 
whose opportunity for selection has been confined to a 
relatively small number of animals. A noted breeder of 
dogs who was asked to give the secret of his success replied, 
" I breed many and hang many." The breeder whose 
operations are limited to a relatively small flock or herd 
cannot expect to accomplish as much in the improvement 
of any class of animals as the breeder handling much 
larger numbers. 

284. Selecting the best. — The improvement of ani- 
mals has come chiefly through selection. In the actual 
process of selection, men have followed various methods 
with the ultimate purpose of obtaining finally a race or 



THE PRACTICE OF BREEDING. 301 

breed of fixed characters, that is, characters which are 
represented by definite determiners in the germ-plasm 
in such a way that the individual animals of the breed 
are able to transmit these desirable characters to their 
offspring with a reasonable degree of certainty. Thus 
many breeders have surrounded their animals or plants 
with exceptionally favorable conditions and have selected 
those which have developed the prized qualities most 
perfectly under such conditions. This was the method 
of Hallet in developing improved varieties of wheat. Un- 
doubtedly many of the early breeders based this practice 
upon a very deep-seated but mistaken belief in the in- 
heritance of acquired characters. This method has been 
very successful in a considerable number of cases, both 
among plants and animals, but not because the environ- 
mental factors involved had fundamentally changed the 
real character of the germ substance. In all such cases 
the improved environment acted merely as an efficient 
selective device and indicated those individuals which 
actually possessed the capacities valued by the breeder. 
This method has often failed in accomplishing lasting 
improvement, because the conditions surrounding the 
breeding stock are not average conditions and the appar- 
ent improvement may be wholly due to a better food 
supply or more room and not due to fundamental differ- 
ences in the germ. Another method of improvement 
which involves selection of the best is to place the plant 
or animal under ordinary or even unfavorable conditions 
and select those individuals which appear best able to 
develop the desired qualities under such conditions. 

285. Selecting chance variations. — We know that 
sudden and important variations often occur in the germ- 
plasm. Some of these variations may be of such a char- 



302 THE BREEDING OF ANIMALS 

acter as to have great economic value to man. Varia- 
tions of this character are invariably transmitted, and the 
wise and observant breeder may often make rapid prog- 
ress by making such chance variation the basis of his 
selections. This is the method of De Vries. In following 
this method the breeder does not consciously undertake 
to cause variation but rather to take advantage of those 
which have resulted from natural causes. The breeder 
of the domestic animals will often have difficulty in deter- 
mining whether a given variation is due to environmental 
causes or is due to fundamental changes in the germ-plasm. 
The skillful breeder, however, will conclude with reason- 
able assurance that when an individual animal exhibits 
a rare and unusual aptitude in the development of a 
certain character or characters, in a herd in which the 
individuals are all maintained under identical conditions, 
the rare development may be regarded as a germinal 
variation. Such germinal variations may under certain 
conditions become the foundation of a new strain. 

286. The Burbank method. — If the selection of varia- 
tions is the road to success in improvement, then why not 
systematically attempt to cause variations and thus 
increase the chances for discovering a desirable mutation ? 
This is the plan followed by Burbank. By crossing a 
great number of individuals, variations are secured, and 
by a process of gradual elimination the outstanding vari- 
ants are retained and reproduced. This plan does not 
create any new forms, but depends on the well-known 
tendency of unit characters to rearrange themselves in 
new combinations which for all practical purposes may 
really become a new creation. This method involves 
the propagation of the improved individual by budding, 
grafting or similar asexual method and cannot therefore 



THE PRACTICE OF BREEDING 303 

be successfully applied in animal-breeding. This method, 
like all the others described, is open to the objection that 
it is after all based on mere chance. It is empirical and 
unscientific. The proportion of failures to successes is 
too great, and for these reasons it is a slow process of im- 
provement. 

287. The mendelian method. — The mendelian method 
is based on the law of dominance and the segregation of 
unit characters. The first step is to determine by the 
behavior of the desired character in transmission whether 
it is a dominant or a recessive character. If it is recessive, 
then it is only necessary to combine two recessives, as 
recessives are homozygous and always breed true. If 
the desired character' proves to be a dominant, it is first 
necessary to determine whether it is present in a heterozy- 
gous or a homozygous condition. If it is homozygous, it 
will breed true. If it is heterozygous, by in-breeding and 
gradually eliminating the recessives it is possible greatly 
to increase the number of dominants appearing and thus 
practically establish a pure strain. This method is also 
more successful in plant- than animal-breeding. The 
animal characters which have come to be recognized as of 
value to man are generally complex and do not behave 
in transmission as unit characters. 



INDEX 



f 



Abortion, 120. 

a cause of sterility, 120. 

agglutination test for, 128. 

contagious, 123. 
* diagnosis of, 127. 

treatment of, 124. 
Acquired characters, 157-160, 162. 

examples of, 162. 

influenced by food supply, 162. 
Acquired diseases, 180. 
Age and fecundity, 96. 

of poultry affects fertility, 96. 

of ram influences fertility, 94. 

of sheep influences fertility, 93. 

of swine influences fertility, 91. 
Age factor in animal-breeding, 271. 
Agglutination test for contagious 

abortion, 128. 
Anaphase in cell division, 12. 
Arkell, 187. 

Artificial insemination methods, 44. 
Asexual reproduction, 16. 
Ash in ration, effect on foetus, 263. 
At wood, 94. 

Bachhuber, 50. 

Barrenness, see also sterility, 119. 
Bateson, 210. 
Beard, 76. 

Beinn Bhreagh flock, fertility of, 99. 
Bell, 99. 
Berberrich, 89. 
Birth, number of young, 85. 
Birthweight of lambs, 262. 
Bitch, genital organs of, 32. 
Blending inheritance, 135. 
Blue-gray cattle, 247. 
Border Leicester sheep, 87. 
Boyd, 249. 

Breeding prematurely decreases 
size, 272. 



Breeding season, 62. 

dioestrum, 55. 

metCBStrum, 55. 

CEstrum, 55. 

prooestrum, 54. 
Brooks, 134. 

Brown-Sequard experiments, 208. 
Brull, 127. 
Burbank method, 302. 

Calcium in rations for pregnant 

swine, 264. 
Castle, 194-294. 
Castration, 22. 

influences secondary sexual char- 
acters, 186. 
Cattalo, 250. 
Cell, 1. 

contents, 4. 

division, 8, 9, 10, 11. 

germ, 2. 

growth, 7. 

structure, 4. 

theory, the, 1. 

the physiological unit, 3. 
Cell division a cause of variation, 

210. 
Characters correlated with fertility, 
102. 

originate in germ-plasm, 195. 
Chillingham cattle, 224. 
Chromatin, 6. 
Chromosomes, 12, 13, 135. 
Cole, 50. 

Color-blindness, 188. 
Community breeding, 299. 
Connaway, 128. 
Contagious abortion, 123. 

complement fixation test, 128. 

diagnosis of, 127. 

treatment of, 124. 



305 



306 



INDEX 



Continuous and discontinuous 

variations, 151. 
Controlling sex, 189. 
Cornevin, 229. 

Corn ration, effect on foetus, 266. 
Cow, reproductive organs of, 29. 
Cows, exceptional fertility of, 107. 
Cross, the first, an improvement, 

247. 
Cross-breeding, 243. 

a cause of variation, 248. 

advantages, 244. 

effect on breeding powers, 244. 

influences fertility, 105. 

permanent results from, 243. 

to increase fertility, 245. 

to increase size, 246. 

to restore constitution, 246. 
Crossing and heredity, 247. 

bison and cattle, 249. 

species, 249. 

Dalrymple, 125. 
Darbyshire, 149. 
Darwin, 52, 72, 90, 146, 198, 210, 

221, 223, 225, 285. 
Davenport, E., 100, 210. 
Decreased size from early breeding 

not transmitted, 273. 
Development, 255. 
De Vries, 152, 302. 
Diagnosis of contagious abortion, 

127. 
Di-hybrids, 155. 
Disease, 179. 

acquired, 180. 

congenital, 181. 

predisposition, 181. 
Duration of lactation, 81. 

of oestrum, 63. 

Early maturity, 283. 

pregnancy, influence on mother, 
274. 
Eckles, 122. 
Evvard, 263. 
Ewart, 122, 168. 
Exercise, effect on lactation, 83. 

favors fertility. 111. 
Experiments by Mendel, 131. 



Factors affecting fertility, 100. 
Fallopian tubes, 27. 

obstruction of, 118. 
Fatness, excessive, unfavorable to 

fertility, 99. 
Female reproductive organs, 24. 
Fertility, 85. 

characters correlated with, 102. 
confinement unfavorable, 89. 
correlated with size, 86. 
domestication increases, 87. 
duration of reproductive period 

influences, 88. 
exceptional in cattle, 107. 
in horses, 106. 
in poultry, 112. 
in sheep, 110. 
frequency of recurrence of oes- 
trum, 88. 
number of mammse as related to, 

101. 
nutrition, effect of, on, 98. 
Poland China breed, 92. 
relation of age to, 91-93. 
relation of gestation to, 87-88. 
Fertilization, 33. 

changes in ovum resulting from, 

36. 
nature of, 34. 
First cross an improvement, 247. 
Flushing ewe, 99. 
Foetal development and heredity, 

261. 
Foetus, size and vigor influenced by 

ration, 266. 
Food supply, excessive, causes 
sterility, 99. 
and body changes, 165. 
influence of restricted, 165. 
Free-martin, 129. 
Function, improvement in, 281. 
milking, 281. 

Galton, 102, 295. 
Gametic purity, 141. 
Gentry, 234. 
Germ-cells, 2, 12. 

origin of, 40. 
Germ-plasm, 161. 

origin of new characters in, 206. 



INDEX 



307 



Gestation, 66. 

causes of variation in period, 72. 

period of, 69. 
Geyelin, 97. 
Goodale, 23, 187. 
Goodnight, 249. 
Graafian follicles, 25. 
Grading, 244. 
Growth, 256. 

a cell function, 259. 

by cell division, 7. 

capacity for, 257. 

development of foetus, 260. 

effect of climate, 271. 

factors influencing, 257. 

impulse strongest in youth, 256, 
260. 

influence of age, 271. 

influence of food supply, 257. 

influenced by early pregnancy, 
276. 

relation of lactation to, 277. 

retarded, permanency of, 268. 

Hagadoorns, 292. 
Hallett, 147, 301. 
Hart, 64, 266. 
Heape, 42, 54. 
Heat or oestrum, 41. 

duration, 63. 

during pregnancy, 60. 

effect of ration on, 64. 

recurrence, 63. 
Helme, 75. 
Heredity, 131. 

and development, 132. 

and foetal development, 261. 

and sex, 183. 

and variation not antagonistic, 
124. 

definitions, 132. 

kinds of, 134. 
Hinny hybrid, 252. 
Huish, 43. 
Humphrey, 64, 266. 
Huxley, 151. 
Hybrids, 249. 

cattle-bison, 249. 

cattle-zebu, 253. 

hinny, 252. 



Hybrids — Continued 
mule, 170-250. 
sheep-goat, 254. 
zebra-horse, 253. 

Immunity, 181. 
Improvement, 280. 

in early maturity, 283. 

in function, 281. 

in milking function, 281. 

in size, 280. 

in speed, 284. 

in tendency to lay on fat, 283. 

in wool production, 282. 
In-breeding, 217. 

advantages claimed, 218. 

bad results from, 219. 

Berkshires, 234. 

cattle, 223. 

Darwin's researches, 231. 

decreased fertility following, 220. 

definition, 217. 

dogs, 228. 

fixing characters by, 240. 

limits of, 238. 

loss of vigor from, 220. 

mice, 231. 

pigs, 226, 234. 

prepotency of in-bred animals, 241 . 

researches of Ritzema Bos, 232. 

results with different species, 242. 

selection important, 238. 

sheep, 227. 

Wistar institute experiments, 233. 
Incubation, fowls, 74. 
Inheritance, 131. 

alternative, 135. 

blending, 135. 

mendelian, 137. 

mosaic, 136. 

of disease, 179. 

of polled character, 144. 
Insemination, artificial, 42. 
Intoxication of male parent, effect 

on offspring, 49. 
Iwanoff, 43. 

Kehrer, 75. 
Kempster, 97. 
Kulbs, 89. 



308 



INDEX 



Lactation, 80. 

duration, 81. 

effect of exercise on, 83. 

habit, 82. 

heredity, 82. 

influence of climate, 83. 

mare mule that secretes milk, 83. 

oestrum, 59. 

relation of food supply to, 82. 

unusual lactation, 83. 
Lambs, birthweight of, 262. 
Langer, 31. 
Law, 68, 117, 124. 

of ancestral heredity, 295. 

of dominance, 139. 

of segregation, 139. 
Lead poisoning, effect on male germ- 
cells, 50. 
Lillie, 47. 
Lock, 133. 

Lord Morton mare, 167. 
Lovejoy, 59, 236. 

McCollum, 64, 266. 
MacFadyean, 124. 
Male reproductive organs, 19. 
Males, milk secretion by, 28. 
Mammae, number as related to fer- 
tility, 101. 
Mammary glands, 28, 81. 

milk secretion by males, 28. 

milk secretion in, 31. 

structure of, 30. 
Mare, genital organs, 26. 
Marshall, 47, 53, 56, 96. 
Maturation of ovum, 13. 
Mendel, 136, 137, 138. 
Mendelian method, 303. 
Metaphase in cell division, 10. 
Miles, 200. 
Milk, 80. 

analysis of milk from mare mule, 
82. 

secretion by males, 28. 

secretion in mammary glands, 31. 
Mironoff, 42. 
Monohybrids, 155. 
Monsees, 72. 
Morgan, 184, 194. 
Mule hybrid, 250. 



Mule hybrid — Continued 

and telegony, 170. 

mare secreting milk, 84. 
Mutation theory, 154. 
Mutilations, 207. 

Nabours, 253. 

Nathusius, 72. 

Nature and nurture, 159. 

Nucleoli, 6. 

Nucleus, 5. 

Number of young at a birth, 85. 

Nutrition influences fertility, 98. 

(Estrum, 41, 55. 

correlated with ovulation, 42. 

duration of, 63. 

effect of ration on, 64. 

influenced by lactation, 59. 

recurrence of, 63. 
Origin of germ-cells, 46. 
Ovaries, 24. 

removal of, 23. 
Oviparous animals, 18. 
Ovum, 13. 

fertilization of, 33. 

Parturition, 75. 

mal-presentation, 77. 

normal, in domestic animals, 76, 

78. 
treatment for mal-presentations, 
79. 
Pearl, 96, 97, 103, 108. 
Pearson, 103. 
Pedigree, 294. 
Penycuik experiments, 168. 
Poultry, age influences fertility, 94. 
Practice of breeding, 280. 
Pregnancy, early influence on 
mother, 274. 
heat during, 60. 
indications of, 66. 
physical examination for, 68. 
Pregnant swine, high calcium 

rations for, 264. 
Presence and absence hypothesis, 

148. 
Previous impregnation, influence of, 
174. 



INDEX 



309 



Primary sexual characters, 19. 
Prophase in cell division, 8. 
Protein, effect of, on foetus, 266. 
Protoplasm, 1, 2, 4. 
Puberty, 56. 

conditions influencing, 58. 
Pure lines, 146, 291. 

Vilmorin's wheat-breeding, 292. 

Ram, age influences fertility, 94. 
Recurrence of oestrum, 63. 
Reduction, 37. 

chromosomes, 37. 

in the female, 40. 

in the male, 41. 
Registered breeding animals, 296. 
Registry associations, 297. 
Reproduction, 16, 183. 
Reproductive organs, of the female, 
24. 

of the male, 19. 
Retarded growth, caused by pre- 
mature breeding, 274. 

permanent effect of, 268. 
Ritzema Bos, 232. 
Rommel, 92. 
Roux, 38, 39. 

Secondary sexual characters, 19, 185. 
Selecting the best, 300. 
Selection, 284. 
aids to, 288. 
importance in animal-breeding, 

286. 
methodical, 286. 
natural, 285. 
Sex, 183. 

effect of age on determination of, 

189. 
effect of nutrition on, 191. 
influenced by maturity of ovum, 

192. 
not controlled by external condi- 
tions, 194. 
proportion influenced by season, 
193. 
Sex-linked characters, 188. 
Sexual glands, transplantation of, 
187. 
reproduction, 17. 



Sheep, fertility influenced by age, 

93. 
Size, decreased by premature breed- 
ing, 272. 

improvement in, 280. 

of litter influenced by age, 91. 
Somatoplasm, 161. 
Sow, genital organs of, 30. 

size of litter influenced by age, 
91. 
Spallanzani, 43. 
Spaying, 23. 
Spencer, 71, 133, 167. 
Spermatogenesis, 41. 
Spermatozoa, 14. 

vitality within female generative 
organs, 46. 
Spermatozoon in fertilization, 37. 
Sperm-cells, conditions influencing 
vitality, 44. 

weakened by too frequent breed- 
ing, 45. 
Steenbock, 64, 266. 
Sterility, 113. 

abortion, 120, 123. 

causes, 114, 119. 

closure of cervix, 117. 

excessive food supply, 99. 

fatty degeneration, 120. 

in the female, 117. 

in the male, 114. 

obstruction in Fallopian tube, 
118. 

twin births (free-martin), 129. 
Stockard, 50. 
Superfoetation, 60. 

examples of, 61. 

Tanner, 104, 116. 
Taylor, 126. 
Telegony, 166. 

possible appearance in mule 
breeding, 170. 
Telophase in cell division, 12. 
Tessier, 70, 72. 
Testicles, 20. 

Theory of pure lines, 146. 
Thomson, 133. 
Thornton, 59. 
Thury, 192. 



310 



INDEX 



Transmission of acquired charac- 
ters, 157. 
Transplanting sexual glands, 187. 
Triplet calves, 108. 
Trowbridge, P. F., 258, 268. 
Twins, 101. 

Union of egg and sperm, 36. 
Unit characters, 141. 
Use and disuse as causes of modi- 
fications, 212. 
Uterus, 28. 

Variation, 195. 

among cows, 203. 

causes, 210. 

continuous and discontinuous, 
150, 151. 

examples of, 200. 

functional, 199. 

germinal, 214. 

infertility of animals, 200. 

meristic, 198. 

morphological, 196. 

physiological, 197. 

use and disuse, 212. 
Verworn, 1. 



Vilmorin's pure line wheat-breeding, 

292. 
Virchow, 2. 

Viviparous animals, 18. 
Von Guiata, 231. 
Von Siebold, 192. 

Waters, 257. 

Weismann, 34, 38, 39, 167, 207, 
210. 

and Von Guiata's in-breeding 
experiments, 231. 

theory of reduction, 38. 
Wentworth, 81, 101, 107. 
Wheat-breeding, 147, 292. 
Wheat ration, 263. 

effect on fcetus, 263. 

effect of mUk secretion, 267. 
Wilsdorf, 230. 
Wilson, 8, 33, 36, 38. 
Wool production, improvement in, 

282. 
Wright, 74, 246. 

Xenia, 176, 177. 

Zebra hybrids, 168 



Printed in the United States of America. 



THE following pages contain advertisements of a 
few of the Macmillan books on kindred subjects 



The Breeds of Live-Stock 

By Livestock Breeders. Revised and Arranged 
By carl W. gay 

Professor of Animal Husbandry in the 
University of Pennsylvania 

Rural Textbook Series. III., i2mo, $1.75 

A more urgent demand, from a constantly increasing number of 
consumers, for animal products must stimulate a greater exploita- 
tion of pure-bred livestock as the source of the seed from which 
market animals and their products are derived. The breeders who 
will get the most out of the respective breeds with which they work, 
will be those best informed as to the inherent possibilities of their 
stock. Study of the origin, history, and development of the breeds 
is, therefore, important. The most successful breeders are essen- 
tially specialists and the most authoritative presentation of the his- 
toric facts, points of merit, and economic importance of the different 
breeds should be expected from those who have devoted themselves 
most exclusively to these breeds. 

Men who have been more or less eminently identified with the 
respective breeds were chosen to prepare the breed material for the 
Cyclopedia of American Agriculture. This matter has been revised, 
brought up to date, and amplified to include types in their relation 
to breeds, and the whole material has been edited, arranged, and 
revised by Dr. Carl W. Gay, Professor of Animal Husbandry in the 
School of Veterinary Medicine of the University of Pennsylvania. 
The original illustrations are reproduced in half tones and the book 
is oifered as the most complete and recent work on the types and 
breeds of livestock. 

THE MACMILLAN COMPANY 

Publishers 64-66 Fifth Avenue New York 



The Principles and Practice of 
Live-Stock Judging 

By carl warren GAY 

Professor of Animal Industry in the 
University of Pennsylvania 

Rural Textbook Series. Cloth, i2mo^ illustrated, $/.jo 

This book has been prepared to meet the demand incident to the 
progress made in livestock husbandry for a more comprehensive, 
thorough, and systematic study of the judging of animals. The 
effort has been made in its preparation to take the student and 
stockman a step further than they have gone heretofore. Part I 
introduces the principles upon which the practice of judging is 
founded ; Part II applies to the practice of judging, definition and 
procedure — the features of animal form to be considered, the means 
of making observations and practice judging by the score card, 
demonstrations, comparative and competitive judging. The bal- 
ance of the work is devoted to special judging, one part being given 
to each of the following : horses, cattle, sheep, swine, the judging 
of breeding animals, and livestock shows. The volume is profusely 
illustrated, typical representatives of the types and breeds being 
shown in untouched photographs of animals to which championship 
honors have been awarded. 



THE MACMILLAN COMPANY 

Publishers 64-66 Fifth Avenue New York 



Animal Husbandry for Schools 

By MERRITT W. HARPER 

Rural Textbook Series. Cloth, i2mo, illustrated, 4og pp., $1.40 

With the increasing study of agricultural subjects in the schools 
has come a demand for a book on Animal Husbandry suitable for 
use by students of high school age. It is to meet such a need that 
this book has been written, and in content, style, and arrangement 
it is admirably adapted to the purpose. It belongs to the Rural 
Textbook Series prepared under the editorial supervision of Profes- 
sor L. H. Bailey of Cornell University. 

In the five parts into which the book is divided the author treats 
horses, cattle, sheep, swine, and poultry, and each is discussed with 
reference to breeds, judging the animal, feeding, and care and man- 
agement. There is also a chapter on the general principles of feed- 
ing. Practical questions and numerous laboratory exercises sup- 
plement the text and compel the student to think through each 
subject as he proceeds. The book is extensively illustrated. 
Designed for use as a textbook, it is also well suited for use as a 
reference book in schools in which time limitations make it impossi- 
ble to use it as a text. 



THE MACMILLAN COMPANY 

Publishers 64-66 Fifth Avenue New Yorl? 



The Feeding of Animals 



By whitman HOWARD JORDAN 

Director of the New York Agricultural Experiment Station 

New edition, igib. Rural Textbook Series 

This book has been revised partly to incorporate the more recent 
knowledge concerning animal nutrition and partly to organize the 
text into a more convenient form for student use. 

As with the former edition, the text is divided into two parts; 
Part I deals with the general principles of bio-chemistry that bear 
upon animal nutrition. Part II discusses the practical side of feed- 
ing animals with attention to such principles as relate specifically to 
the nutrition of the various classes of farm animals. It is expected 
that by this arrangement the volume will be useful for classroom 
work with those students who have given little or no attention to 
bio-chemistry as such, at the same time the interest is served of 
those students who have given considerable attention to chemical 
studies. The popular reader who is familiar with the general prin- 
ciples of agricultural science should also find this treatise helpful in 
the practice of animal husbandry. 



THE MACMILLAN COMPANY 

Publishers 64-66 Fifth Avenue New York 



